Hi Dave,  Without seeing the bird (foot) and having specific details
as to the size and configuration (shaping) of the existing foot, no
one will be able to help you too much.  It's kind of like calling an
auto parts shop and saying you're looking for a radiator fan belt for
your 1960's German motor car without identifying the make, model, year
or engine size.

For your information, some German manufacturers did not put feet on
their mechanical birds.  So, the simplest solution is to remove the
remaining foot leaving the bird "footless" -- no one else is likely
to notice.

That being said, in all probability, the feet/foot of the bird was made
from a relatively short (1" to 1-1/2 inch long) pieces of twisted
copper wire.  The claws/talons of the bird were created by unraveling
a little bit of the twisted wire and shaping them to look like talons.

If you don't already have some appropriate electrical wire around the
house, go to the local hardware store, and get a foot (12") or so of
copper electrical wire (of the same gauge/diameter as the existing wire
foot), then strip off the plastic or rubber insulation and fashion a
replacement foot to match the one you already have.  The original foot,
will have darkened with age; ergo, you might want to make two new feet
so they will match each other exactly.

Best of luck with your project.

Don Caine - Proprietor, The Music Box Repair Center Unlimited
Lomita, California
http://www.musicboxrepaircenter.com/