Bob Forrest (Thelonious Monster, Bicyle Thief) recently shared a lot of audio files on Archive.org. One of the uploads stood out; a Thelonious Monster show from September 23, 1988 including John Frusciante on guitar. The show was held at the Cal State Fullerton Pub.
John was supposed to join Thelonious Monster but on October 5th, 1988 joined the Red Hot Chili Peppers instead.
Check out the show here.