Bingo. Most of them buy raw powders from a supplier who carries it and then add the other ingredients such as oils and sterilization compounds such as BA or other types of alcohols. I only know of a handful of people who deal with powers and as far i know it could all be originating from the same place. The labs could be set up like an actual chem lab or it might be made in their kitchen.. or a bathroom, basicly unless you know them personally you probably wouldnt know what their lab looks like. Most of the stuff you get online is from UGLs, I've seen claims made by a lot of online sites stating they have pharma grade Test. But I've never ordered it. If you find a ugl that's been around for a while you'll find plenty of reviews on different bodybuilding forums to speak on the quality.
I used to get my test. legally from my endo, but like the guy above and beach bum mentioned its quite expensive. Even with insurance I find it a hell of lot cheaper and easier to order it from a UGL.
When I'm not doing a cycle I only spend about $10 a week for my test this way.
I used to make my own from raw powders and bottle it up. It was great because you mix and match until you get the formula the way you like it. Its pretty simple to do, and much cheaper then using a UGL if you plan on using a lot, or you have friends that want to chip in on the powders and help make it. It's not hard to make a sterile product even your doing it in a home lab.