We live in a world of wonderful electronic wizardry with greeting
cards, toys and many other gadgets able to imitate a broad range of
music and common sounds.  It just so happens that I recently bought a
"stocking stuffer" magnetic note clip which made a loud "ribbet" frog
call when pressed.  Others in the range included hens, roosters, Klaxon
horns, dogs, cows etc.   All these sounds were a good resemblance of
the original and best of all, the cost was just a few dollars.

For your purpose, Bob, they could be triggered mechanically or elect-
rically and are small enough to fit into a tight space.  You could
readily hold a few spares since this sort of thing is likely to be a
passing fad.

I bought it at a local department store.  E-mail me for more details.

Cheers,
Darrell Clarke,
Adelaide, Australia