Lost & Found
Create a playlist called Found, select everything in Music and drag it into the Found playlist (it may take some time to count the tracks that are to be dropped). Create a smart playlist called Lostmatching All the rules Playlist is Music and Playlist is not Found. Your lost tracks will be in this playlist. You should be able to select all the tracks in this playlist with CTRL-A and then remove them from iTunes with CTRL-SHIFT-DELETE.
Or use iTunes Folder Watch with its option to check for dead tracks on start up.
However if the broken tracks are duplicates of non-broken files then I've written a script called DeDuper which can help remove unwanted duplicates, merge ratings, play counts and playlist membership, and remove dupes with dead links as long as there is one real file to merge the stats to. See this thread for background. I also have a tool called FindTracks for fixing the broken links if the files are sill there but not quite where iTunes is looking for them. For more details see this thread.
tt2