It sounds like you're looking for flavors that will be used for only single flavor mixes, correct? You're not looking for the individual "flavorings" that you combine to use in a recipe of multiple flavorings?
If it's the first type that you're looking for (which is the easiest form of DIY and quite a few people do that), I've heard that OSDIY...
Your one stop shop for flavorings ...has some really good One Shot Flavors and One Shot Blends. They come in 3 different sizes, too! Some people have said they only use 3-5% and it's great when mixed with their own PG, VG, and Nic. Others say they usually use about 10% of some of them to suit their taste.
I've seen people post about especially liking these One Shot Flavors from them: Blue Raspberry Slush, Strawberry Milk, Olde Time Root Beer, Pink Lemonade, and the Blue Pom. In the One Shot Blends...favorites seem to be: Lucky Shot and Blue Note.
One friend has raved enough about the Lucky Shot, that I'm going to try a bottle of it. I've always made my DIY eliquids by following a recipe or coming up with my own using many flavorings, but he's convinced me to try it.
If you're talking about mixing several flavorings to make your own mixed Flavor...I buy all mine at Wizard Labs. However, there are many places online to buy them. I just like WL because they're competitively priced, are great quality IMO, have a huge variety from many manufacturers, and their care in packaging and shipping is superb!
Whichever it is that you do though...I'd
definitely stock up on nic base, preferrably the 100mg/mL Nic, so you can make the most finished bottles of eliquid out of it. Just make sure to freeze it for the best preservation. Many who DIY either already have, or are making sure they DO get, enough to last them for however long they think they're going to still be vaping. I have enough to last me 6-7 years already, at my current usage rate and 6mg nic level. I still plan to buy at least another liter of it!
