When you find one source that is helpful for your research, it often can lead to other useful sources. Strategies for finding more sources based on what you have include:
Browse the bibliography or references at the end of a relevant book or article. 
Credo Reference mentions this strategy in a brief video about finding relevant sources (if you are off campus you will have to log in to view the video).
If you find a relevant book in the catalog, click on the title to see the full record.
Then click on relevant subjects or on the author's name to see more works by her/him.
Use Google Scholar's "Cited by" link to find out who cited the relevant work.
Or click on the author's name for other works by her/him.