I've had great success using the Bookfinder.com site which searches new and used inventory of bookstores around the world..
This site's worked out great for me finding a few old and out of print books I was seeking also I've found it a good way to compare pricing of current books too..
Here's the link..
http://www.bookfinder.com/
Like Google the more info you have cuts down on resulting 'hits' but if you don't know the author or complete name of the book etc, less is better..
Good luck!.
~ Pete