Not really what your asking for, but my $.02.
For tangs in particular I would try to shop local. Given that in general they are quite ick prone, and have relatively fast metabolisms, I'd want to see the fish and the system it's in before buying a tang.
Mail order you don't have any idea of the condition, fatness, size, and likelyhood of parisites. Of course a reputable E-tailer is better than a not so reputable one, but it can still be a bit hit or miss.
If your after a hard to find tang, or otherwise must go online, I have had very good exp with
http://www.exoticfish.com/
What I've gotten from them has been better than expected, AND I've gotten honest answers from them about something I've been considereing ordering. I've called on numerous occasions and talked with Jeff the owner, he's told me not to buy things because they don't look so good right now exct. IME not many e-tailers will be honest if the fish you want isn't looking good.
No matter what you do, I suggest using a proper QT process with any new tang. If I get one I'll do a full hypo treatment even if I see no sign of spots. Better safe than sorry, esp with a screen name like yours
.