Honestly, and I can't stress this enough, university librarians/research librarians should be your best friends on the planet when you're in college (is this for a college level course?). Most major universities have access to hundreds of historical databases, and depending on where you are in the country (or if your school is a Federal Depository) their archives are extremely useful.

Edit: I say depending on where you are in the country because most university archives house material gathered from the surrounding area. For instance, you're not going to find a lot of information on the California Gold Rush in Auburn University's archives.