http://www.rockauto carries a re-ring kit from Sealed Power, but it does not include pistons or rings for boring anything over stock. You can get pistons and rings for a variety of sizes of overbore from rockauto though, and yes you do need larger pistons if you bore the block.
Just a quick estimate of the cost for parts:
Full Kit with economy rings $160
4 pistons 4x$30 each
premium ring set: $55
Total $355
I figured the full kit with the cheap rings, since they are stock size and you'd be getting larger pistons/rings anyway.
JCWhitney sells about the same kit I believe. Sealed Power is the only company I know of for sure that makes a rebuild kit, so odds are good if you see one elsewhere it will be the same thing. They are part of the Federal-Mogul family of companies, including Fel-Pro gaskets. I've always been happy with gaskets I've gotten, but I've never took the plunge and bought done a full rebuild.
You also see kits on ebay fairly often, though that is less of a sure thing.