Quote Originally Posted by David Ruby
One idea I have is to see if filters for other similar TLR's might fit, as they seem to be more prevalent. The filter seems to have three flanges that you seat then twist to lock onto the lens. Does anyone have any idea if this might work?
Sounds like a Bay 1, in which case you're in luck. Bay 1 (aka B30) is the standard filter mount for Rollei and Yashica TLR's. They're pretty easy to get hold of, but often cost more than they realistically should - walk away from anything more than a couple of pounts and you'll find another for a better price.

There's a pic of a Bay 1 on my website - follow the link below, and go to articles -> Filters. It's written about the baby tlr's but they use the same filters as the larger ones.