Deleting unfound files in iTunes quickly

I had a mess. after an external drive failure, I had to reimport my library to Itunes. Now a huge number of random duplicate files are listed in my music library. Not all have the ! next to them. I need to analyze my library and have it tell me which songs the file can't be found for and delete those. I am afraid to show duplicates and remove them because many of them do not have files and itunes will remove the song that actually has a file leaving me with a long list of songs that can't find the music file. ideas?