Don't want to rain on your parade, so to say, but just stumbling upon an A. crassipinnis is a local fish store is not likely plausible.
Admittingly your enthusiasm is commendable. It's great to see that you've taken the time to look up the fish on the net. In your research, you've probably noted where these fish come from. Commerical collection and exportation of crassippinnis very seldomly occurs.
I am definately not saying that if I have not recently imported it, then another importer who supplies your local store couldn't possibly have done so.
Anything's possible. But plausible? The odds are extremely unlikely.
So unless you saw them labeled as 'rare Bolivian wild oscars', or something like that, you'll just need to consider the odds of actually finding this species given the circumstances.
But please don't let this diminish your enthusiasm of searching and caring for the fish. I hope that your enthusiasm is contagious and others will take the time to research their new fish as you've taken the time to do so. It's encouraging (and reassuring as well) to read of this still occurring.