You can find a book without knowing its title by searching for the author, the ISBN or even relevant keywords online. Alternately, you can try a local bookstore to ask a professional or an online book forum to see if the community can assist.
Bookfinder.com is an excellent resource for finding a book. Its search feature allows you to enter an author's name or the ISBN of a book. It also has a keyword search under Show More Options..., allowing you to do a free-form search of its database. If you prefer to ask someone for assistance, both online forums and brick-and-mortar bookstores provide an excellent resource of knowledge. The former provides a wide audience of people who may be familiar with what you're seeking, and the latter provides professionals with extensive literary knowledge.