If the Graduate Center does not have the book you need, you can have the book sent here from another library.
Are you affiliated with multiple CUNY campuses? For example, do you study at the GC but work at another campus, or maybe even two other campuses? If so, you are entitled to remote access to library e-resources (e.g., databases, e-journals, e-books) from all of your affiliated campuses. Different CUNY libraries have different e-resources, so check all of your affiliated libraries (via their separate websites) for the e-resources you need!