The databases listed below are good sources of academic journal articles in Political Science & related topics.
Using them (rather than Web sources) will greatly improve your chances of producing high quality work.
Also useful are review articles, which summarise research on a topic. Look out for these, or try adding keywords like "review" in your searches. Many journals produce them, and some specialise in this area, notably the Annual Reviews series of publications. We subscribe to the social sciences collection, which includes the Annual Review of Political Science.
Other sources that could be useful:
International Political Science Abstracts - this journal summarises articles published in academic journals. It's published every two months by the International Political Science Association. You can search by keyword on the publisher website to find details of relevant articles on a topic. You can also sign up for alerts when each new issue is published.
Observatory of International Research (OOIR) - free table of contents service for key academic journals indexed by the Web of Science database. Covers political science & related areas. Useful current awareness tool, though without alerting facility. Basic search available