Lulu is running a 40% off sale:
Here are some books you might consider:
* * A • Le Moyne Gospel Acclamations (172 pages)
* * B • Couture Gospel Acclamations (172 pages)
* * C • Keyboard Accomp. for Resp. Psalms (401 pages)
* * D • Goupil Graduals (288 pages)
* * E • Lalemant Polyphony (229 pages)
* * F • Matri Divinæ Gratiæ (42 pages)
* * G • A New Book Of Old Hymns (92 pages)
* * H • Campion Organ Accomp. (374 pages)
A whole bunch of modern polyphony scores are available at Emporium Kevin Allen.