My understanding is that the show organizers don't allow things such as BC's, Tanks, Regulators, etc... to be sold because of liability issues. These things are life support systems in essence and the show organizer doesn't want to have any liability with products sold at their show. I bought some gloves from the seasoft booth while I was there, so things like that and other "accessories" are available then and there. the other stuff you have to basically mail-order while you're standing in the booth.
I can certainly see where they're coming from, but I wish it didn't have to be that way. Jengineer, I fully agree, they seem to hide the fact that these things can't be purchased directly at the show, all of the shows I go to (Chicago, New Jersey)are the same way.