call them up. Ask for promotions from the phone menu. Even if you are under contract, one of DirecTV's current offerings a rep can give you is a "sports package" that includes Fox Sports South (and the rest of the regional sports networks in the 600s).
DirecTV prorates any changes to you service so you also could upgrade your TV package for the game, call them back the next day and you'll just pay for the difference in cost for that day. They should be able to keep any of your current discounts intact with plan changes.