Bill Edgerton asked about 48-key music books for Piano Melodico.
Le Ludion in France produce new books and have quite a repertoire:
http://www.leludion.com/ventecartons/ 

You will, however, need a smattering of French since most of the web
site is not available in English, although it is fairly obvious what
information they require.  Replies from them by e-mail will be in
English.

John Farmer, UK