Sorry to beak this to you, guybrush, but there is a secret club. Many of us are members, and we know where there is a barn full of Mark IIs and M-300s as well as a huge stash of M-400s. We leak them out on ebay every once in a while.
Until you get offered membership, I guess you're going to have to hunt for them the way I used to... with a bow and arrow. Bow hunting is pretty easy, but you have to have good aim because once spotted, Mellotrons of any model move very quickly.
So what is a "guybrush?" I hesitate to think.
bush lover