They're as scarce as hen's teeth or chicken lips or whatever else is impossible to find. I recently did a workshop where two other Mamiya 7 users had them and I discovered that it really is a must have.
For you, it is a must have. I've never needed more than a decent ballhead for the M7II. Be that as it may, apparently there are (expensive) choices: http://acratech.net/product.php?productid=71
Thanks for that ROL. It's good to know that there are options. I do prefer the Kirk L-Bracket as it doesn't have to move up and down and won't get in the way of the shutter curtain on the Mamiya 7ii. My ball head does swivel to the side, it's an Arca-Swiss so it's not a cheapo one either. I still find the bracket a more convenient and stable option.