This script will allow you to select a "dead" file track in iTunes (designated with the (!)) and attempt to locate a file using Spotlight that corresponds to the selected track's Song Name, Artist, and Album, and then replace the dead track with a file from the search results. All tag data, including artwork, is preserved from the original track selected.
Designated as a Retro Script because: never very efficient to begin with, the script is less so under modern circumstances.
(See the application Music Folder Files Not Added.)
OBLIGATORY WARNING! Because this script has been designated as a "Retro Script" there is no guarantee that it will function as described and may even corrupt or destroy data.