One of the more difficult MSA disc sets is the 1976 Red Barn issue.
As far as I can tell, the discs were given out at just this one location in Kenosha, Wisconsin.
The set consists of the 70 players that were in all the different MSA disc sets from 1976. Four or five of those are Cubs. The questionable Cub is Andy Thornton. He has discs in the sets that show him as both a Cub and an Expo. The TCDB shows him with the Expos in their listing of the Red Barn set. Is it possible that there is a Cub version for him? I have no idea. I've never seen his as a Cub, but since these are so rare, that doesn't really mean anything.
I have three of the four for-sure Red Barn Cubs.
I've had the Cardenal and Morales for a while. I recently was able to get the Rick Monday. I saw it in a listing for a lot of nine Red Barn discs. I asked the seller if he would sell me just the Monday and he agreed. The missing Cub is Bill Madlock. I hope to find one soon... but I'm not holding my breath.