Like @Beamslider said, Just buy any 0nic juice from any juice maker and add the appropriate nic to make the 6% you are looking for.
I buy NS from Nicotine River and they have 3 throat hit levels. Hit NS, Normal NS, and Smooth NS. It's pretty obvious what they are. I like the smooth and vape at 6mg also. The smooth has almost no throat hit at all and is probably what you are looking for. A 150ml bottle of 100mg/ml is about $11 and will last quite a while, probably 6 months or more depending on how much you vape daily. A 30ml bottle of 0 nic off the shelf juice will only need about 1.8ml of nic to make it 6%.
The only caution is 100mg/ml nic is dangerous if not handled properly. Watch some mixing videos and use a juice calculator to give you the amount of nic you need to add to get the 6% you want. There are lots of free juice calculators around, many online so you don't have to install one if you don't want to, but use a calculator and get a couple of syringes (for the amount you'll be using for either 30ml or 60ml bottles of juice, a 3 or 5ml syringe with a blunt tip will work out fine. Or you can spend the $21 and get a digital scale from Amazon that can measure to 0.01 accuracy. Either way will work great. You should probably get some disposable nitrile gloves just for safety.
I switched over from FB to NS a while ago and think NS is a better choice because not only can you tailor the nic level you like, but you can choose the throat hit characteristic you prefer. As far as nicotine they are both the same in that regard. They are just different methods of extracting nicotine from a tobacco plant.
So just buy 0 nic juice and DIY nic. Quite easy to do and just might temp you to start mixing your own juices, which is the real fun is for many of us.
6 mg/ml does NOT equal 6%..