The best source for out-of-print books is
www.abebooks.com. You can order through abebooks.com, or go directly to the seller. You can enter the title or author for your search criteria. I've found all books bought through them to be exactly as advertised. You can get some truly pristine copies.
I used to use
www.bibliofind.com, but they were taken over by Amazon.com, and then they left their server wide open so that hackers were able to get their customers' credit card numbers. I told them I didn't appreciate that!
Hope this helps!