Update:

For anyone needing a useable fully adjustable rearsight for the Remimex Mito, the later block one (designed for 11mm dovetail) from the HW77 will fit. I've just bought one for mine. Avoid the earlier type as it has a locating anti-recoil stud and I don't think will fit. Used, they're about for between £30 and £70, and are a good alternative to the (now) defunct Falcon Fn rearsight.