When you find a book or an article that is relevant to your topic, always check the bibliography or the reference list of that source cited by an author for other sources and then ask a librarian for help with finding them. This process is called "Bibliography Mining" or "Cited Reference Searching".
Please take advantage of it, as the author of the book or article has already done much of your topic research for you, and they spent many weeks/months/years of his/her life doing research.