Im sure that any mower shop in your area would have some second hand decompressors around. Unless they scrapped all their mowers including rare early Victa 18's, (without telling me. Not mentioning any names) Or they might be too lazy to get a 3/4 spanner out and take one off and try and sell you a new one.
Another option would be find one off any older 160cc engine as Blumbly said. You just want to get one that is repairable with clips and not the newer sealed ones (garbage).
If you still have no luck I may be able to help.
