Here is a list of a few farms that grow and make sorghum: http://goo.gl/Hq4bs
In Asheville you will definitely find Sorghum at some of the holiday tailgate markets, for example both the Holiday Bazaar at the chamber of commerce lot and the Asheville City Market on Saturdays in December until the week before Christmas. Ingles has carried Deal Farms sorghum last year but I've not heard about that yet.
Wherever you find it make sure to ask good questions or buy direct from the farmer. There are jars labeled "sorghum syrup" that are mostly or all flavored corn syrup.