South Dakota does not have licensing for guides. Odd but true. Antelopin' is a do-it-yourself hunt in the Rushmore state.
For Wyoming, try calling the large ad taxidermy shops in Sheridan, Douglas, Casper, and Gillette. They'll put you in touch with a good guide.
Jack Atchinson of Worldwide Safaris books a number of quality hunts. A little on the spendy side but 100% reputable. You can count on a good bed, good food, quality vehicles and equipment, competant guides.
Plan on early October. Best hunting is opening day when the herds are not scattered and spooky.
Jack