There's a trick I just tried with itunes 11, I don't remember the details for a previous (better) version of itunes.
To summerize the trick I detail bellow it's to use a video field to set for all your music tracks, then have itunes set it and check all tracks, itunes will set it only for tracks with a valid file and will update the track state to show whe it hasn't a file. Then you can use that field value to sort tracks of you library music and delete all tracks with a missing file.
So for itunes 11.0.1:
- Select your library in itunes to see all tracks.
- Then choose the tracks presentation.
- Then in Prensentation options add the serie (video section)
- Sort the list by Season to check it's not a used field, it shouldn't as its music.
If the season field isn't used then you can use the trick :
- Select all in the list
- Get information
- Go in Video Tab
- In season number enter 1
- Then check ok.
- Then let itunes set the field for all tracks and it will check them all. It takes times if you have many tracks.
- Once it's finished just sort the list by season, and all tracks with no season are those with missing file. Well perhaps also those with a protected file that can't be changed. Ididn't tested that last point but you could give a visual check to the elements to be sure that all are showing the icon for missing file.
So with that sort you can select all the tracks with missing file to delete them.
Then you can restore the season field to none to reset all valid tracks:
- Select all tracks in your library
- Righ click to get information
- Select video tab and in season number field erase the 1 you set before.
- Ok to apply.
Well it's neither fast nor without risks of human errors, a paid software well designed and well programed is a wiser choice, but that manual process is free of money (well if time isn't money).
The small adventage I can see is in that way you are sure that itunes will check all files of your library.
EDIT: Take care when you do the operation that all the removable disk you are using to store files in you itunes are well connected. That's this sort of little traps a human could forget check and it could generate a little disaster. :-)