You might try here:
http://report.bookfinder.com/
The BookFinder.com Report is a different kind of bestseller list.
It's a measure of the most sought after out of print titles in America.
BookFinder.com has been online since 1997, enabling individuals, libraries, and book dealers to track down and purchase books, new or used, in or out of print, rare or readily available.
Volume 1 of the BookFinder.com Report is based on our analysis of aggregate trends for out of print book searches between July and December of 2002.