Use FTP search! FTP search, unlike web search, will link you directly to files on the 'net. Try looking for MIDI with a *.mid search type. You'll easily come up with more than a million files. When you look for MIDI on web sites, you'll never be guaranteed of having a direct download.

Quick tutorial on how to maximize your search:
Note: you should ALWAYS use a wildcard in the search line. This will grant you maximum results. Generally, you should use multiple-substrings case-insensitive search to gather results. And, if possible, try to use an FTP search engine that is minimalistic with regards to pictures and advertisements, because it speeds up your search results.

-First, start out with a descriptive name for your object, eg. dungeon*.mid.

-Next, if the results don't satisfy you, hack off some of the letters, eg. dung*.mid (specifically chosen for this reason =)

-Search again. If the results still don't grant success, you can try abbreviating, or shortening once again, eg. dng*.mid or dun*.mid.

-Remember, the smaller the filename, the more results you'll get. If you make the filename too small, you'll get too many results, but if you make the filename too big, you won't get enough results at all. Try to find a happy medium.

Lycos Fast FTP Search: I recommend this one, it's fast and easy.