Quick-O muffler does some decent work. I've heard alot of good things about West End muffler in Newport, TN. There's another place toward Oak Ridge, but I don't know who it is. Call Terry at Performance Products, 865-689-4700. He can tell you who it is.
I also know a guy who just had some work done at a place on Western Ave. Let me know if you want more info, and I'll get it.
Since you're in the Chatty area, a buddy of mine from GA always uses a guy over the state line in GA. He's an old-timer and does work at his house, and does "cash only" work. Again, LMK if you want more info.