Chainsaw Repair

Ebay is full of 44 parts saws in various stages of disassembly. I bought one of the earlier models to fix my mid 80's saw. I had inadvertently dropped a tree on it and split the plastic fuel tank . That was 3 years ago. Now I need the piston and jug because I managed to score the piston while ripping slabs for benches out of mesquite stumps. I am in the process of trying to deglaze the cylinder. I also would appreciate a hint as to what ring will fit that piston. It is a Mahle 42 ZD 5 jug. Is there a cross reference to anything that old.
John