Artie has it right. In general you need to know approximately WHERE and WHEN the file existed
Unfortunately, that's exactly the problem. I don't know precisely where it would have been located, or when the file was created. Though, I'm beginning to suspect that it's much older than I first thought, and probably was done on a very old computer that was never backed up with TM, and if the file still exists, it's probably on a CD backup somewhere. Yuck!
Regarding the warning not to directly search the TM backup drive, why would this be a problem as long as I only do this to locate the file, but not change anything?