I just got an unmetered prism for my Mamiya 645 1000s but need a -3 diopter as i don't like to shoot wearing glasses. Diopters for the newer Super/Pro/TL-prisms are widely available, but i couldn't find any -3 for the older ones.

I already checked Ebay, KEH, B&H etc. and sent an email to Mamiya Germany but didn't get a reply yet. Does someone know a source for the old correction lenses or if there are some diopters from other cameras which will fit?

Regards,
Matthias