I would:
A) call the cfc and ask if they would be willing to send your contact info to the current owner if you can provide the serial number (they'll never tell you the other guys info), then,
B) concentrate on finding the serial number, first place I would try is the smith who did the work, maybe he has it on file, I would also ask the cfc if they can search your file for past ser numbers, and lastly, if it was bought new, try S&W.
Good luck,
Lupo