Books on Solresol

• Gajewski, Boleslas
  Grammaire du Solresol, ou langue universelle de Fr. Sudre
  Paris: 1902 (44 p.)
  English translation of Gajewski's book, courtesy of Stephen L. Rice
  Vocabulary and a mini-dictionary derived from Gajewski's book, also courtesy of Stephen L. Rice
• Sudre, Jean Francois (1798-1866??)
  Langue musicale universelle
  Paris: 1866 (480+ p.)
  PM 8008.S94
  Raw scanned pages in PDF format

Hopefully both are out of copyright by now.