Dear Mr. Rumson,  you're right, Hindemith and others composed works for
reproducing piano.

Data from the "Donaueschinger Kammermusiktage 1926" of July 25, 1926:
the following "Originalkompositionen fuer Welte-Mignon" were published:

Paul Hindemith (1895-1963) (rolls no.4107 and 4108)
-Rondo, from Klaviermusik Op.37, Fassung fuer Welte-Mignon-Klavier
-Toccata Op.40,1 fuer Welte-Migon-Klavier

Gerhard Muench (1907-?) (roll no. 4109)
Polyphone Etuden fuer mechanisches Klavier
  I: Introduzione Maestoso,II: Prestissimo, III: Largo, IV: Jazz,
  V: Andantino, VI: Fugato.

Ernst Toch (1887-1964) (rolls no. 4103-4106)
-Drei Studien fuer Welte-Mignon-Klavier.
-Der Jongleur, Fassung fuer Welte-Mignon-Klavier


In the Welte-Mignon catalogue of 1927 the following titles were
published:

Hans Hass (1897-1955)
-Fugen-Capriccio (roll No.4150)
-Intermezzo (roll no. 4151)

Nicolai Lopatnikoff (1903-1976)
-Scherzo (roll no.4152)
-Toccata (roll no.4153)

There are different others composition by Hindemith for mechanical organ,
but the works seem to be lost.  There are also other composers for this
instruments, but this all would be to much for a fast email.

In the journal "Das Mechanische Musikinstrument" No.36, Okt. 1985, are a
few articles about Nancarrow.  The instruments of Nancarrow and his
atelier and rolls are now in Basel in the Paul-Sacher-foundation in
Basel.

Kind regards from the hometown of Welte-Mignon

Gerhard Dangel-Reese
Augustinermuseum
Salzstr.32, D-79098 Freiburg
fon *49-761-201-2528, fax *49-761-201-2597