If it says A123 on the label thats all that matters- stay away from more generic looking versions that just say li-ion or lifepo4 without the A123 badge.
Best bet for genuine A123s is tanicpacks.com, though hobbycity do cell individual cells too yeah:
clicky
The prices have gone up quite steadily for a while, I remember when they were more like $10 about a year ago, it was just the high shipping costs that was annoying back then...