According to some recent researches, Memphis Tour and Travel who organizes those tours, isn't even known at the Memphis Visitor Center. So they might not even exist (that is one more trap for the tourists).
Memphis:
At Blues City Tours, you can book all kinds of tours.
Nashville:
You can take a Greyhound bus on Union Ave in Memphis, and take a sightseeing tour once you are there.
Tupelo:
L & A Tours organize tours to Tupelo
(having enough people on those tours of course)