I get my mirrors of a guy on eBay , user ID is Marty1107 .
If he doesn't list the one your after he will cut one to size for you .
When fitting , don't forget the blue side is a protective covering for the mirrored side and not the back if the mirror .
Remove the blue plastic and that side faces up .
People have said they've fitted a new mirror and found it to give s double image and incorrect focussing .
That's because they they left the cover on and fitted it back to front .
I'm in the gradual process of replacing the mirrors in most of my box cameras and TLRs , between than and a new ground glass ( if needed ) it makes the cameras truly usable again .
It's surprising how degraded the mirrors get over 50 to 100 years !