I don't know what you have done in the way of research on "how" to DIY but start by reading this:
Begin Here
Once you have an understanding of safe nicotine handling, for you and all those around you, and decide you are willing to behave accordingly;then you will want to figure out WHAT recipes/flavors you want to try and make (see final paragraph).
Then you are ready to go shopping.
You will need:
1. A recipe calculator of some sort. This will assist you with the arithmetic and give you someplace to keep notes.
(A note on "notes" - Make lots of them. It doesn't matter how; just do it! Some will use note pads or note books, others will use a word processor program like Office or OpenOffice (free-ware), others will put their notes right in the recipe files of their calculator of choice (when available). Notes are important because they remind you of what you did, how you did it, and if it did, or didn't work. Notes are one of the most important tools you will have to get repeatable results.)
As for juice/recipe calculators; you have choices here: (these are far from the only ones available. Just some of the more popular/common ones. If you don't care for any of these; please do your own research.)
You can use an on-line calculator like the one found at
e-Liquid Recipes. (a caution here: these will want you to create accounts and or donate/purchase to save your own recipes. Also most have limited functionality)
Or, if you use a windows computer, a lot of ECF community folks like
EJuice Me Up. (near the bottom you will find "Free Software." Click on "Download now" and follow instructions.
Personally I use a calculator created by
@HotRod19579 found
here.
I like this one because it has a very nice inventory management component that EJMU does not. Also HotRod19579 maintains a very active thread
here on ECF for assistance and continuing software development/improvement.
Speaking of ECF members offering other calculator choices; another that has been spoken well of (though I have not used it personally) is by
@Scubabatdan and is in Microsoft xls spreadsheet format. You can find it
here. And
here is the link to his discussion thread.
I am afraid I have no links for Apple compatible calculators as I am not an "Apple" person.
2) You will need a means to measure your ingredients. Most DIYers measure by volume or weight. Volume is the cheaper (at least for initial investment) of the two as you can start with a few syringes and a few blunt tipped needles ($5-$10 worth?)(I recommend a minimum of 2-3 each of 1mL, 3mL, and 5mL {10mL, and 25/30mL if you are making larger than 15mL batches} plus 2-3 14 gauge {for VG} and 18 gauge {for PG & flavorings} blunt-tip needles). If you're going to measure by weight you will need a digital scale able to measure to 1/100 of a gram (0.01g) which you can find on Amazon ($25-$40 and up?) (afraid you'll have to research that on your own because I measure by volume). And you will still need something to transfer fluids from their container to yours... like syringes or pipettes.
3) You will need something to measure into. This can be as simple as cleaned recycled bottles of e-juice you have saved, to beakers, and flasks, and all manner of bottles sold all over the web. It just depends on what you want and how much you want to mix at a time.
4) Finally you will need the e-juice components. PG, VG, flavoring, and nicotine solution (NEVER use higher than 100 milligrams per milliliter (100mg/mL)! And, if you are not sure about that, you may want to start even lower.).
5) Oops! One more finally. You will need something someplace to store your mixes and supplies that is
protected from heat, light, children, and pets. Again, this can be as simple and inexpensive as a shoe box on a top shelf of a closet to as fancy and expensive as laboratory-grade refrigeration units. The choice is yours.
Now that I got that off my chest I can finally answer your actual question about suppliers; It depends on how you want to shop. If you want the absolute-rock-bottom price on each and every item... you are on your own. Expect to spend tens, if not hundreds, of hours google searching for them. If you want a single supplier that will have all/most of what you need to
at least get started... I can tell you who I have used with satisfactory results (they didn't steal my personal info, and didn't gouge me on price) and I still use them, at least in part, for my continued shopping.
I have used (for "all-inclusive" orders):
Wizard Labs - They carry PG, VG, nic solutions, several different flavoring manufacturers, and glass and handling gear.
Things I like about them: They really do have everything you need to start on their site; They are reasonably quick with turn time (my orders normally arrive in 1- 1 1/2 weeks); Their on-line inventory seems pretty accurate (if they are out of stock on something they will note it both in the individual product page as well as your shopping cart); They offer several TFA flavors that are not even shown on TFA's website (not sure if these are exclusive or not); They offer a pretty complete line of each of the flavoring mfg. they carry; all flavors are offered in 8mL size (most for less that $2) and ship in glass bottles.
Things I don't care for: Free shipping is a little high at $65 minimum; rarely do "sales" (this can be a mixed bag as a lot of vendors that do frequent sales simply have bloated "regular" prices); Nicotine is definitely not the cheapest... but for starting out you can purchase in small quantities and know you are getting a good (if not great) product; they don't offer a digital scale if you want to measure by weight; They don't offer Flavour Arts as one of their flavoring lines (a popular manufacturer).
One Stop DIY Shop - They have a smaller offering than Wizard but have enough that you can get started with a single purchase from them. I have also found them to be cheaper on bottles, syringes, and needles. They do not offer nicotine above 48mg/mL but they do have it (and the 36mg/48mg choices are not bad choices for first time DIYers).
Things I like about them: The have unicorn bottles (a tall, slender, plastic bottle with a very narrow tip, good for carrying in pocket and short term storage) in both 15mL and 30mL sizes at a great price ($0.50/ea. either size); they carry Flavour Arts; fast shipping (all my orders have been at/or less than 5 business days; offer a pretty good range of flavor mfg..
Things I don't care for: smallest flavor size is 15mL to 30mL for most of their lines (that a lot to toss if I don't like it vs. Wizard's 8mL sample size); limited nicotine choices; no digital scales; No Inawera flavoring offering (another popular mfg.).
I have also used
Bull City Vapor for some Inawera flavors I couldn't get from Wizard labs. But I am not sure I would list them as all-inclusive; their mixing gear is pretty limited (NO needles other than 18 gauge which are no good for VG) and they no longer offer ANY nicotine. But they have a great flavor selection and many people here on ECF swear by them.
Other vendors that I see mentioned (in a good way) on ECF frequently but have not yet personally used and can't vouch for (and in no particular order):
RTS Vapes
Vapers Tek (no mixing gear)
ecigexpress
I'm sure there are many others but these are ones that I have seen ECF folks talk favorably, and often enough, for me to bookmark them as potential future vendors
for me. Hopefully others will chime in and share their own experiences with vendors they like and would recommend (you probably have 5 additional posts in the time it took me to type this out).
A couple of final thoughts. Start out small; with your purchases, and with your batch sizes (I personally suggest starting with 10-15mL batches) until you become comfortable with your technique and your ability to duplicate results (remember to take notes for every step) AND that DIYing is even for you. You will also not be wasting a bunch of product on recipes that sound (and are good to others taste buds) good on paper, and even have good reviews, but for what ever reason just don't float
your boat. Once you home in on what works for you; then you can buy larger quantities and mix larger batches and you are off to the races.
With all the FDA noise in the news, and on the boards, resist the urge to buy liters and gallons of mixing supplies until you learn if DIYing is for you (unless you
know you have someone to sell it to, or pass it on). We still have a couple of years access if stockpiling is your thing (and I'm guessing at least a couple of months before prices start to rise. No vendor wants to be "that guy" who was the tool that gouged at first opportunity).
If you really want to be economical with your starting inventory; do an ECF search for "Bill's 100DT method." It is a method that uses 1 drop to equal 1%. This will make really small test batches that will let you try it and see if you want to make more. It does require a little patience as you have to be willing to watch and count to 100.
Do lots of research, there are some really great threads on here, and ask lots of questions
if you can't find the answers, as there are also a lot of good people on here that are happy to help. (But please be courteous and at least try to see if someone has already answered your question by doing a few key word searches.)
Don't quit after your first attempt. Most first-time DIYers are not thrilled with they're first (or second, or third, or ???) attempt at mixing. Ideally, if you have an idea of the flavors you like to vape, search ECF and Google for recipes for that flavor (even if its a commercial brand/blend; there are quite a few "clone" recipes out there). Try to find several/many recipes (a) your not going to like all of them (if any) and (b) you can also get an idea of what flavorings you will want to order on your first order. One of the biggest plagues to the DIYer is someone posts a recipe that sounds terrific only to find you're one ingredient short.
So have an idea of what you want to make AND what you need to make it BEFORE you go shopping. It will save you buying flavors that sound really good but you have no idea where to use them.
Have fun! Keep trying. And Welcome to the world of DIY
Unfortunately, I never was able to break the habit, my last order put me over 300 flavors. 
