The only 24 Mamiya ever made for their 645 line is a manual focus fisheye with built-in filters.
Not wanting to hijack Leo's thread, but I own one and it is a relatively rare lens to come by. It is an excellent lens optically, and has a more "gentle" fisheye appearance than the typical 15/16/17 fisheyes for 35mm. It works quite well with digital sensors too...
Cheers,