PetSmart in Gainesville Fl, about two years ago. It was maybe 2 full inches when I first got him.
It grew up in a 45g, got to be about 4 inches, and last Christmas bumped him up to a 100gal, and he's grown at least a full inch since then. It still could be a dwarf, but I think he was just growing slow from being in the smaller tank.
For size ref, those two sillies are about 4 inches diameter. ( and at least a full inch thick)