Yesterday, BookFinder.com issued its annual report on books that are "out-of-print and in demand," i.e.

Book Fair
(937) 999-4491
The Dayton Book Fair is the largest sale of second-hand books in the Ohio region, (more)
Book Dealer: Antiquarian & Rare
(775) 322-6657
Zephyr Books, named for the Zephyr winds that blow through the Washoe Valley, (more)
Book Dealer: Antiquarian & Rare
(845) 264-7256
Via Biblio.com: mathematics & science; history of science; first-edition fiction (more)