EDIT: Oh, and to clarify, do you mean the real FFIII or the American FFIII that is really FFVI?
FF3 (in American numbering terms) was out on the SNES, and got released in the UK as Final Fantasy VI for the PSX, and it came with a demo of FFX. If you’re lucky, you can find it in Game, or try their online store at http://shop.game.net/ and see if it’s in stock there.
I hope III comes out for PSX sometime. My collection looks a little sad with a gap for it in.