Most parking at the stadium a permit is required, a map is located here:
http://www.gopack.com/auto_pdf/p_hot...ng-lot-map0910
However, there are other pay places available.
Parking lots open 5 hours prior to kick off for the permit lots, I have no idea if the other lots follow the same.
Far as I can tell you can't purchase a single ticket online but you shouldn't have an issue finding a scalper or buying on stubhub.