Some great databases to start your research are Academic Search Complete, JSTOR, and LexisNexis Academic. When searching it is best to avoid using "pro" and "con" in your search terms (unless the issue usually uses it, e.g. "Pro-life"). As you become more familiar with the argument adjust your search terms. Lastly, many times the articles that seem to support the other side of the argument may provide very valuable information about the side you are researching. For more information, check out UGL's guide on making pro/con arguments.