Doug, from my own experience, start by finding the winemakers. Find out if there's a local wine competition, like at the county fair, or a local winemaking group. Find out who is in charge of it. Ask them.
If your experience is like mine was, I started out with no sources for muscadines. Then I searched the Net and found some in a 50-mile radius. Then I found some smaller vineyards close by through the county fair wine competition, just talking with folks entering. Now I have 2-3 different possibilities close by, with concord, Norton, muscadine and scuppernong choices. That's about all the grapes that can be grown this far south.
So it just evolves as you ask around. BTW, typical 2012 muscadine price here was $6/$7 a gallon U-pick.