MEGA BUMP.
While I won't take back everything bad I've ever said about GameStop, I have to give credit where credit is due.
I used their online tracker to call about 10 different stores that claimed they had the 3DS version of the Collector's Edition version of Adventure Time in stock. Finally found a store in Michigan that has it! And they're shipping it to a local store just for lil' ol' me. Thanks, GameStop!
($10 says it's an open copy that no one bothered to tell me about... but, whatever... beggars can't be choosers, eh?)