65Corvair

I know it may be a long shot (firearm pun intended) but a shotgun ghost ring rear sight may fit on the MR1. Below is a link to LPA sights, that look very similar, but not the same as the original MR1 rear sight. My assumption is since Benelli main business is shotgun, the receiver shape and hole spacing for the MR1 would be the same as one of their shotguns. http://www.lpasights.com/en/products/shs02r/