At one time most of the Viper Sites had them but they are not linked, and they are basically not used, not recorded, and lots of them don't respond if you try to key them up. I went around with a Motorola Viper radio that was programmed with all the 7tac and 8 tac frequencies (I was a federal government emergency manager) and I ran across a few but randomly. Try putting them in a bank on your scanner and see what you get. I have never heard them actually used myself in the Durham area, Greenville, or Northeastern parts of state. I think Durham had one, Greenville did, and Ahoskie.
Regards Richard