I know nothing about their program now but I did walk on to George Mason's track team in the fall of '88 with high school PR's of 50.2 in the 400 and 2:02 in the 800.
Having never talked to a college coach while in high school, 2 weeks into the fall semester I asked the assistant coach (Joe Showers at the time) if I could practice with the team. He told me to get a physical and come back. So I did and then asked the head coach (John Cook back then) about practice. He also told me to get a physical. When I told him that I had one, he sent me to train with the sprinters.
A couple of years into it I eventually made the relay team, placed 7th in the 800 at IC4A's and won a watered down conference 1500 whiling picking up some scholarship money.
Mason had one of the best programs in the country at the time and I never saw them turn away anyone that wanted to run for them. There are plenty of local meets to run in including ones at their own facility, particularly indoors.
That being said, I don't see any reason why you couldn't walk on to Mason with your credentials.