Now that you have a thesis statement and a better idea of exactly what you're looking for, plus the vocabulary you need to find it, it's time to GO DEEPER:
- Return to the databases you used in your initial research, but try the ADVANCED search tool.
- Mix and match your search terms.
- Find articles that match or come close to your topic, then look at the SUBJECT terms attached. Add these to your search list.
- Mine the bibliographies of the books/articles you've found for other books/articles on your topic.
- Use Google Scholar to find out who the experts in the area are - look at the "Cited by" numbers: higher number=more authority. Find articles by these experts.
- Look for the missing pieces - use your outline to determine if there are gaps in your research or places that your argument needs support.
- Take notes directly into your outline - match what you find to your established argument.