Finding out of print books is a challenge for the mystery book fan. Some ways that have worked for me are:
Used book stores.
The Poisoned Pen (www.poisonedpen.com) – A great mystery book shop in Scottsdale Arizona. They have an online store. A very knowledgeable staff, that will do book searches for it’s customers.
The Paperback Swap (www.paperbackswap.com) – An online book exchange. Get credits by passing along your excess books. Use those credits to acquire from other members offers. You can post your wants, and when they come into inventory you get an Email offering you the book. Only cost is postage when you send out books.
Amazon (www.amazon.com) – search their inventory for out of print and collectible books, by author.
Good luck in your search!