First, identify the Disciplinary Focus. What subject areas (beyond your main subject and PPA) are involved? To help identify the areas, brainstorm keywords for your research question/thesis.
Second, what General Sources might help you with your thesis? This includes:
Third, explore the Topical Databases (right column) in your subject area. Don't forget about resources available via the open web such as organizations, NGOs, and governmental bodies as well as legislative sources.
Fourth, tie this research together by exploring the PPA Databases available via the "Secondary Sources" tab on the right.