When you find a few relevant articles or books, use what you have found to find more sources for your research. Here are a few strategies:
Browse the bibliography or references at the end of a relevant book or article entry in a reference work.
If you find a relevant book in the catalog, look at the Item Information to find Subjects that lead to more books on the same topic.
Use Google Scholar cited by link to find out who cited the relevant work. Or click on the author's name for other works by that author.