At the agency we keep lists of people's tapes. Along with the lists, we store what the owner has said about DAT/Analog (this is usually evident from the lists though) and trading for blanks.
When someone asks about a particular tape, we go through the lists in search for it. Upon finding it, we pass on the owner's identity to the person asking. (This is, of course, after the owner has volunteered to be refered to.) We try to distribute the owners we refer to a little, so the first person who has a lot of tapes not always is refered to.
Long detailed lists of wanted tapes are usually not serviced in detail, a few likely contacts are given to get the person started. The agency works best for people searching for shows they attended, where they met their wife, or other specific events they have been unable to track down among their regular sources.
We have also been helping out tape trade newbies, pointing them to a person willing to trade blanks.
If you like to participate, send your list of tapes (Date, venue etc, songlists are not neccesary nor prefered.) Please tell if you do NOT wish to trade for blanks, and be sure to mention if you're using DAT, if it's not clear from the list.