I had a mirror (beamsplitter) custom-cut to size for a Yashica 35YL by Knight Optical because the original was uncleanable, and was replaced during a "CLA" with one from another camera that was 3mm too short, so you could see the mirror support clip through the VF:
http://www.knightoptical.com/php/bro...cat=407&catClr=
They did a great job even if it was a bit pricey (the shipping cost as much as the mirror). Unfortunately I cannot find any info on how to adjust the RF itself which is still wildly out of whack (and seems different from other models of silimar vintage - the YL was not made for very long) so I'm just guessing off the distance scale on the lens
BTW the other posters are not wrong about the coating on the original mirrors being delicate - I've never seen anything like it for fragility.
HTH,
Scott