Just had a squint at Abebooks,
http://www.abebooks.co.uk/ some oldish books:
Rameau - Jean Malignon (1960) £2
Jean-Philippe Rameau: His Life and Work (1970) (ISBN: 0486214168) - Cuthbert Girdlestone £2.22
Reflexions sur l'Art et la Vie de Jean-Philippe Rameau (1683-1764).
BERTHIER, Paul £14.95
Rameau and Musical Thought in the Enlightenment (ISBN: 052161709X)
Christensen, Thomas Foreword by Ian Bent, (2004) £22
Élémens de musique: Théorique et pratique, suivant les principes de m. Rameau, éclaircis, développés et simplifiés (ISBN: 0543949974)
Jean Le Rond D\\\'Alembert (2002)
and look at THIS by the man himself:
Elements de Musique theorique et pratique, suivant les Principes de M. Rameau, eclaircis, developpes et simplifies . Nouvelle Edition, revue corrigee & considerablement augmentee. ALEMBERT, Jean Le Rond de' (1772) £600 !!!
Treatise on Harmony (ISBN: 0486224619) - Rameau, Jean Philippe (Author) Gossett, Philip (Translator) £6.63
DEMONSTRATION DU PRINCIPE DE L'HARMONIE SERVANT DE BASE A TOUT L'ART MUSICAL THEORIQUE ET PRATIQUE PARIS 1750 - Rameau, Jean-Philippe (Edition 1930)
some music too
Complete Works for Solo Keyboard (ISBN: 9780486278476) - Rameau, Jean-Phillip for £2.92
Twenty Sonatas for Piano Solo (ISBN: 9780757919022) - Rameau £2.71
Jean-Philippe Rameau ( 1683 - 1764 ) Pieces De Clavecin with the composer's original appended texts unabridged and with several facsimile reproductions
Rameau, Jean-Philippe [ edited by Erwin R. Jacobi ] £14.00
also
The Rules of Musical Interpretation in the Baroque Era (17th - 18th centuries) common to all instruments. Translated by John Lambert.
VEILHAN, Jean-Claude (1979) £15.95
French Baroque Masters (New Grove Composer Biography) (ISBN: 0333390229)
James R. Anthony, et al (1986) £4.74