Yep, the aircraft camping registrations will sell you everything you need: campsite credentials, admission wristbands, programs, tiedowns if you forget (but please don't). If you're in something other than GAC/GAP, you're inside the gates when you park anyhow.
Likewise, Scholler does the same thing. Pretty efficient operation over there the one year I camped there. You just had them your credit card and back comes your stuff. Don't even need to get out of the car.
Note that you will need your EAA number (you must be a member to camp). However, they got computerized a few years back so they don't have nay problem looking you up if you don't have your card (Or haven't committed the number to memory). If you don't have a membership, they'll be glad to sell you one.
By the way, I don't know how HBC handles things, but if you want your participatin plaque and mug in Vintage, you need to be a vintage member.