Southland Gun Works in Darlington, SC. Directly across the road from the Darlington race track (NASCAR).
There are actually 2 great smiths in the area. There is another shop, Darlington gun works, whose smith, from what I've heard, is world renowned for building custom rifles. I called and asked if they sold lower receivers the other day and the woman said, "No, we don't sell or work on AR-15's". Shocked me. I guess they have plenty of business working on long guns..