I love Civ 2. Possibly my favourite game ever. I was getting pretty good at the game, too. I don't know about Civ 3, but I have CIV 4. I don't play it that much though. Never even touched any of the expansion packs that came with the game. But it seems faithful enough and has a ton of features.
Can't help you with downloads. For buying a copy, try Amazon. Shouldn't be hard to find.