Currently being updated and expanded...

• Seminary CO-OP (new books only)

• Bibliofind (search engine)

• Advanced Book Exchange (search engine)

• Dr. Rudolf Habelt GmbH

• Casalini Libri (new books only)

• Zentrales Verzeichnis Antiquarischer Bücher (search engine)

• BookFinder.com (multiple search engines)

• De Rooy Booksellers

• Archeologica (Rome)

• Antiqbook (search engine)

• Archaeologia (Oakland)

* I have used many of these and have no complaints, but your results may vary.