The scale of the 12-note Rolmonica is as follows:

  E F G B C D E F G A C B

The top two notes are shown reversed, with the top C being the 11th
note up.  This unusual arrangement is correct.  The roll is 3-1/4
inches wide, with the lowest note on the right when playing downhill
off the back of the spool.

This scale, and over sixty other small scales, is shown in The Organette
Book by Kevin McElhone, published by the MBSGB.

For a roll-playing harmonica project one could also check out the
16-note chromatic rolls made for the Chromatic Rolmonica, Play-a-Sax,
Melody Player, Fireside Player, Plarola and Nor-Cos.  These play variants
of the same roll with slight spool differences and variations to the
positions of the top notes.  These scales are also given in the book.

An alternative would be to use organette rolls where you would have
a much greater choice of music, but would also end up with a much larger
harmonica!  I suggest the 14-note Jubal Orchestrone or the 16-note
Musette.  Rolls could be cut down into individual tunes and respooled.

Good luck, and best regards from the UK,
Nicholas Simons