There are two people in the U.S. whom you might contact about parts
for bird boxes.  One is Ray Lins, Burnsville, Minn. (R.lins@att.net).
The other is Moe Goldy, Port St. Lucie, Fla. (mgoldy@earthlink.net).

Griesbaum in Germany used to be known for its whistlers and bird boxes,
and the Wendel family is still supplying parts and making whistlers, 
at least, using some of the Griesbaum tools.  You can learn more from
their web site,  http://www.musicboxworld.de/

Matthew Caulfield