Existem alguns ótimos AppleScripts disponíveis em dougscripts.com . Para remover entradas inválidas, você pode usar Super Remover Faixas Morto v2.1 .
O que faz:
Surveys iTunes for tracks whose files are no longer available (as indicated by a "!" next to their names) and removes them. Any playlists that subsequently contain no tracks will then be deleted. Progress is displayed every 500 tracks.
Para procurar novas faixas, você pode usar Biblioteca do iTunes Sincronizar (um script do Automator):
Place the script in /Username/Library/Workflows/Applications/Finder (where Username is your username)
If the workflow directories don't exist, you have to create them manually.
When done, the script will be available to you with a simple right mouseclick (on some free desktop space).
Select Automator -> Synchronize Library and your done.
Note: When running this script for the first time, open Automator and disable the “Date Modified” rule because we want to add all the songs first. When done you can enable the rule again.
Ambas as ferramentas estão disponíveis gratuitamente.