I'll let y'all hone your Googling skills :-) but a search for DVD or CD cataloging freeware utility should yield something. I'm almost positive there are apps that will create and maintain a database of removable disk contents for as many as you have. Instant search and bam you know that File X is on Disk 23 in folder yada yada. Probably included in some backup software.

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken