Gary, I have several castanet actions here in the shop.  I have also
had one made that actually worked like a castanet player which was far
more complex than the standard nickelodeon castanet action.  It went
3 taps on the female pair and one tap on the male pair: pa, pa, pa, PUM.

I will look my castanets up and get them out.  I also have some pipe
organ actions.  When you want to see something in the player realm,
we have most of it right here in St. Louis.  Have you ever visited us?

Usually a standard reiterating pneumatic will work well without
alteration for the standard action arrangement.

A set of castanets have a high pitched pair and a low pitched pair.
The high one is termed "female" while the lower pitched pair is called
"male".

D.L. Bullock    St. Louis
http://www.thepianoworld.com/