Just a thought, but have you talked to any machinists or tool makers? They might be able to make a die for you, or modify one that is close to the right size. Might be a little hard on the wallet, but you never know. I worked with a guy in alberta that made all kinds of parts and pieces for his remote control planes and boats, unreal what he could do with a lathe. Actually, that may be a good place to start. Any good hobby store would probably know of a machine shop that specializes in small parts production.