Dear friends,  If you still haven't located diaphragms for your
mechanical bird, you may wish to contact S. La Rose in North Carolina,
http://www.slarose.com/

I purchased a set of diaphragms from them a couple of years ago.
I don't see them listed on their web page, but if you give them
a call, I bet they still have them in stock.

Best wishes,

Mike Walter