Mellotronists

I just remembered something that has been bugging me for a while:  On 
Zappa's Hot RAts there is a great sorta carousel sound on the 
song "Return of the 
Son of Mr Greengenes", or is it just "the Son Of..."? Anyway, if you 
know the record its just a really beautiful and dramatic 
carnival/boardwalk (depending on your childhood experience with a 
carousel), sound.. It sounds like it was played on a keyboard but I 
am not sure.. Liner notes say something about an "Organus Maximus" 
but with Zappa I a cant tell if this is serious.. Whats the point you 
ask? I really want to track this instrument down so that I can make 
some tapes for my MK VI... Also looking for anyone in northern that 
can play Bass Harmonica a la Pet Sounds.. Thanks

Derrick Espino