If you can't find a book at the SRC or in one of our premium databases, look for it online. You may be able to find it for free or see a preview: the table of contents, introduction, and even complete chapters. When full books are available, they tend to be old—out of copyright and in the "public domain"—but occasionally you can find recent books in their entirety.
If you find only a preview, it may be enough to help you determine if a book is useful for your research and worth finding at a local library, requesting through Interlibrary Loan (if you are off campus you will make ILL requests at your local library), or buying. Previews can also be useful if you're waiting for textbooks to arrive.