Where can I borrow books that my own university's library doesn't have? I need a book for my teaching and/or research, but my university's library doesn't have this book.  I don't think I'll use it enough to justify spending money out of my own pocket to own it.  What other ways should I try?  I searched Internet, there is no "free" (in whatever sense) PDF of it either.
Ask your university librarian.
Usually universities libraries collaborate with each other. They can look whether the other universities have the book (I know this happens within Canadian universities)..