Finaid.org is a good place to start with information about the different types of aid that is out there and how to obtain it. Fastweb.com is also good -- you create a profile and they match you to scholarships and grants in their database.
You definitely want to contact the financial aid office at the university. Many schools have a universal scholarship form you can fill out and they'll consider you for any you qualify for. True, many scholarships are for undergrads, but the money is there for graduate students -- you just have to work a little harder to find it.
You may also want to contact the department you'll be in to see what aid and scholarships they have for incoming grad students and what the deadline for all those applications is.
You can always do it the old-fashioned way and look through the books in the reference section at your local library. Tomes are published every year about where money is and they are often categorized by field of study, gender, and there are some for re-entry students and non-traditional as well.
Leave no stone unturned. You would be amazed at some of things that you can get a scholarship for.