If you don't have a place where you archive all project files, my suggestion would be to do global searches of files with the .fcp extension. Once you locate that and open it, you will see the names of the missing files to help you relink them. Alternatively, do global searches on capture and scratch.
There's more to it than that.
If you capture video from tape, or via Log and Transfer, it captures the media as Quicktime files inside the CAPTURE SCRATCH folder onto the drive you designated as your CAPTURE SCRATCH in the FCP SYSTEM PREFERENCES. FCP will separate the media by folders with the project name.
That folder, and the render files, and any audio or pictures you use in the project is what you archive. If you don't know where they are...well...dunno how you are going to find them. If the clip names match the media file name...then you can search that way.