The Pell grant is not available for graduate study. Only those that have not earned a bachelor's degree are eligible for Pell grants.
There are no federal need-based grants for graduate school. There are some loans (such as Perkins with a fixed rate of 5% which is, at the moment, higher than the Stafford loan rate) that are need based.
Your best bet (as always) is to check with your school's financial aid office. They will best know of the grants, scholarships, and loans for which you are eligible.