I went through this a while back and gave up. Look at Suntour forks for something similar. The travel on virtually all new forks is more than yours and will change the geometry for better or worse. Rigid forks are another option. I disassembled my fork to attempt a rebuild and while inserts/springs/etc are available or hackable, the elastomer or whatever was melted and welded to the inside of the fork and no solvent would remove it. Head over to MTB forum and see what other folks have done. I sold my M2 and got a 90-91 rigid Stumpy.