In Florida I've been to a few repticons and there's usually little options for racks. One company brings a bunch and that's it. Cserpents is listed as being AT shows but it seems like aside from the really big ones they just have another vendor bring the ordered racks for customers to pick up.
But the show I went to in Denver they had like 3 guys selling racks, and one was a pretty cool one for hatchlings to juveniles while the other two had more variety.
So looking up vendors before hand and contacting them will be the best idea. You won't get a "deal" on a rack but you'll make sure you get the exact rack you want. I went to the repticon in Tampa when I had one snake, I bought 2 more snakes and I really needed a rack. My only option was a combo 15qt/32qt rack and I really wish I would have just gotten a bigger 28 or 32qt rack.