Once you have searched the Pace Library Catalog and the ConnectNY catalog, try searching WorldCat. Books you find in WorldCat may need to be requested on ILLiad Interlibrary Loan. WorldCat.org lets you search the collections of libraries in your community and around the world.
Google Books allows you to search for books new and old. If the book is out of copyright, or the publisher has given them permission, you'll be able to see a preview of the book, and in some cases the entire text. If it's in the public domain, you're free to download a PDF copy.