I haven't been involved in mb's long, but it seems to me there are to many variables to each build, and to many frame type's to make anything available for resale. I made this specifically for my Columbia Klunker after making a totally different design to mount the same motor to my Felt Bixby.
The only way i could produce this at a price point for resale would be to make in quantity and sell from inventory, then, the first time someone, who's never picked up a wrench before, has trouble making it work for their scenario and post something negative i never sell another and get stuck with the inventory.
I appreciate that those who have been doing this awhile like the mount!