With such a long running series, many of the books are now Out of Print and can only be found through used bookstores or online services such as Amazon.com. Hopefully the whole series will eventually become available as eBooks.
Some of the information on this Chronological Bibliography comes from http://www.spiretech.com/~dafoxx/books/y... and Saint-Germain Tribute Page http://members.optushome.com.au/velvetsp...
You may be interested in the Saint-Germain Chronology available on these websites.
In order of historical periods.
DARK OF THE SUN (@ 2000 BC / 535-537) Published 2004 (#17) After traveling across China and Asia, Saint-Germain returns to his home, possibly to die. Provides a glimpse into his early life and how he became a vampire.
OUT THE HOUSE OF LIFE (1495-523 BC / 1825-1828) Published 1990 (Madelaine de Montalia #1) Out of Print Madelaine de Montalia fulfills her dream of exploring the ruins of Egypt, aided by information from Saint-Germain.
BLOOD GAMES (79-71 B.C.) Published 1979 (#3) Beginning during the reign of Nero, Sanct' Germain finds his way through the political turmoil of the time, and becomes the lover of the incomparable Atta Olivia Clemens.
DARK OF THE SUN (535-537) Published 2004 (#17) Sangi-Ragozh is a merchant in China, when, unknown to him-or anyone else in most of the world-Krakatoa explodes in a massive volcanic eruption. In the months to come, the world grows colder and darker as the massive cloud of dust and ash spreads across the globe, blocking sunlight. Sea trade is ravaged. Crops fail. Livestock, and then people, begin to starve. Disease spreads. Panic rises. As always in times of trouble, foreigners-and the vampire is always a foreigner, wherever he travels-become targets. Fleeing toward the West, where he hopes to find safety and sanity.
A FLAME IN BYZANTIUM (545-551) Published 1987 (Atta Olivia Clemens #1) Out of Print Atta Olivia Clemens, forced to leave Rome, journeys to the Constantinople of Justinian and discovers how much she has lost.
COME TWILIGHT (620-1130) Published 2001 (#13) From his first affaire with Csimenae in 622, Saint-Germain is caught up in contention with her; this is not lessened upon his return to Catalonia a century later, when she has created her own tribe of vampire. This book focuses not on a particular point in history, but on a particular character and place, Spain, over a period of about 500 years.
NIGHT BLOOMING (Charlegmagne's reign 800) Published 2002 (#15) Out of Print