Home Depot, et al., should have spools of wire, yes.

Most DirecTV installations are grounded at the drip trap, which is where the cable is looped into kind of an S or cloverleaf shape in order to keep water running down the length of the cable from grounding things by creating a local minimum in the height of the cable, usually using a female-to-female connector. If yours doesn't have this, then you may have slightly more to consider than just simple grounding.