You could do this in script. There may already be one out there - check scriptspot.com , or Neil Blevins' blur script packs, I recall his having material editing / management scripts in them. Or write one yourself :)
Definitely check for the script as MoP suggests first, but if not there are a couple of ways to minimize the pain. This is a bit of work but can help in tracking down which maps/materials are used on which objects. Click a blank material slot. Choose Get Material. Browse From Scene. Show Maps and Materials. Now you should…