Bascially any of the older Camaro's/Firebird's below 1973 will be generally harder to find and a little more expensive, but pretty much every part you could ever need for those cars is easily available (the Nova is about the same, although from what I've seen they are a little cheaper to buy).
It seems most older Chevy cars have bigger reproduction parts resources, compared to say.. Mopar (Dodge). It's usually better (and easier) to start with something that is complete (minus an engine/transmission.. especially if you plan to do a swap anyways), but it depends on what exactly you plan to do with it.
Really if you wanted something that you can drive at the same time you are also restoring it, then that's not a bad way to go, as you can enjoy it while you gradually make it better.
You can ask anyone and they'll tell you it's a long hard time and money consuming thing when restoring an older car (especially if you come along unexpected problems).. but in the long run it's worth it (if you have the will to finish what you start), and it's something you can enjoy and take pride in.
I don't know what really to tell you other than reading and talking to people that are more experienced is the best way to start out and get some ideas. Good luck to you, hope you find what you're wanting and enjoy making it what you want.