There's a couple of places you can catch badge sales after the fact:
-
https://reddit.com/r/PAXPassExchange after July 1st will have people posting their badges for sale, and always at cost.
- Usually a few weeks before PAX, Penny Arcade does a resale of badges they collect from scalpers, so you can keep an eye on those.
I also might know a guy who has some passes on sale most likely in late July.