Ed, over the past few weeks I've made lens caps for many of the spurios non standard lens I own often from Bakerlite lids off old chemical bottle/jars. I'll see what I have this afternoon.

Your other alternative is to make a lens cap from card and then cover it, Tomosy has a section on making them in his book on Restoring Classic Cameras but there's articles online. These can match the big Schneider lens caps in terms of quality.

Ian