I don't really have a link, but from what I understand, (which of course is not proof) eXtremeVaping uses synthetic nic, and what I've heard on the chat with Volcano is that other than the Tobacco Pure, the rest of their USA juices are synthetic.
Levy may use pharm grade nic, but not synthetic, even if that is what he is saying. You would not be able to sell synth nic juice for the prices Levy has. And it would be 50:50 l-nic:d-nic, and d-nic is not as active as l-nic, so it would not be as good. Synth l-nic would be several orders of magnitude more expensive than extracted and purified pharm-grade nic.
And text typed into a chat does not equal chemical fact.
To be fair, I think some vendors may not know the difference between pharm-grade nic and synthetic, and think they are the same thing. As long as it is l-nic, they are the same chemically, but the production costs to make the two differ dramatically, indeed prohibitively. You really do need a pretty strong background in synthetic organic chemistry to understand why the costs are so different.
Nothing against you, as you are just relating what you have read/seen/heard to the discussion. This is a very central and important matter however, and I think it is important to not let info like this propagate, since the vast majority of people have little to no education in chemistry, and I have already seen info like this used to fool customers into thinking they are getting something special when they are not.
Many Chinese juices use grades cheaper than pharm-grade, and so many other tobacco compounds come along for the ride from extraction. You can taste them. Pharm grade nic is the same thing, just with more purification steps, and it essentially pure l-nic. That all said, I think Levy's nic juice is about as good as can be obtained, but it is almost certainly not synth nic, nor does it need to be to be so good.