I found 7 different ones at my local gamestop today...97 cents each! Only 2 were sealed though. I came home, and one (Nuclear Throne) had already been redeemed, but the rest were good. Unfortunately that was the last copy of Nuclear Throne....but for 97 cents the steelbook and soundtrack are worth it. Game looks good, so I'll just pick it up during a steam sale.
Considering the code was stored with the disc, not on the floor...it looks like it was probably an employee who redeemed it :/
Edit: Just saw the game discs are DRM free....so I can still play Nuclear Throne... Sweeeet. Would have been nice having it on Steam though.