When you find a book that is relevant to your topic, ALWAYS check the bibliography for other sources and then ask a librarian for help with finding them. The author of the book has already done much of your research for you, and he/she spent many weeks/months/years of his/her life doing research. Take advantage of it!
Cross-reference these books in the OWHL Catalog and NOBLE and request books that are not at Andover. Or see a librarian for help!