I've never been to one of the conventions, but have always wanted to go too. That flag sounds totally awesome. I have one of the 25th anniversary flags that were hanging on the lamp posts that I bought on ebay.
However, one of the coolest things I ever encountered was way before the ebay craze, I was in MGM studios by the backlot area and on the street which now has the SF skyline view they had all these booths set up selling off all sorts of old merchandise and park signs. I bought a white lucite Mickey's Birthdayland sign that was hanging on a pole which is now Toon Town for $20 and a MK 15th anniversary foam core sign for $15. This was way before disney became hip to the idea that they could sell this stuff for big bucks to the conventionears.