+1 Dioptre for Contarex

A somewhat obscure request. Who can help me acquire a +1 diopter eyepiece correction lens for a Contarex? I can only measure with a rule and it seems it could be a 15mm ID/16mm OD thread. I don't mind if it takes the form of a just a piece of circular optic that could be held by a collar. Any assistance greatly appreciated.

Check with Edmund Optics they custom make lenses etc.

http://www.jeffreyglasser.com/

Contax and Yashica (same??) made round diopters with no frame. Just the glass. I used a "Contax" labled one on a Rolleiflex SL35M by gluing it to the eyecup holder works very well.