I am also seeking book music for a Piano Melodico, but for the 73-note
model.  Bill Edgerton mentions that there were three models of 30, 48,
and 73 notes respectively.  However, this site mentions a fourth model,
the 75 (Verdi): http://www.pianomelodico.com/english/music.htm 

The site also seems to indicate that newly produced books can be
bought; however, I have not attempted to purchase any because I have
yet to determine whether my customer's instrument is even restorable.

John Grant