Along with the library catalogue, the databases listed below are useful for finding academic articles in Politics & IR published in reputable peer-reviewed journals. Using these resources (rather than Web sources) will 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.
International Political Science Abstracts is a journal that 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.