Ebay if yo can find one. These are really hard to find, from what i learned the kits on ebay that include the piston and 1 of each gasket are for the later years compressor. There are some sellers that sell individual gaskets but getting ahold of a complete rebuild kit is next to impossible. Classic industries has it on there website but it has been out of stock for a while now.
I ended up rebuilding my RV2 compressor and it actually worked well converted to R134, but I ended up deciding to delete my AC. I may list the compressor for sale soon.