A lot of major yards- almost never wandering out....Chattanooga , Tn......Bellvue, Oh....... Inman Yard down in Atlanta...Sheffield Yard in Muscle Shows, Alabama....Luther Yard in St. Louis......On railpictures.net there is evidence of one going from Memphis to Chattanooga- where I presume they are all based.....
http://www.railpictures.net/viewphoto.php?id=34441
I was thinking of buying one in N, but then I noticed they would never come in my area as the farthest north they go is Bellvue- they would take the line through Cincinnati for servicing in the Chatt............