I have an old Ica Sirene 135 plate camera for 9x12 glass plates that I'd like to start using, unfortunately the retaining ring for the lens got lost. I have a retaining ring that came with a 90mm Angulon that I have (the old one in the Synchro-Compur shutter) that is the right diameter, but I can't screw it on all the way. Any idea where I can find a ring that fits?