I would suggest
The Sioux Trading Post (Prairie Edge) in Rapid City, South Dakota. They do a lot of business with the native people in that area, both buying and selling. I have ordered from them online, and also visited their store a few years ago.
Maybe also
Taos Herb Company. I have ordered from them, and they are good folks.
Kinnikinnik, specifically, is bearberry (
Uva ursi). Another herb that was used a lot on the plains is red willow bark (
Cornus stolonifera). I have bought it from Sioux Trading Post, and Taos Herb normally carries it, but neither of those places have it right now. There is an outfit called
Medicine Man Crafts in North Carolina which appears to have red willow bark in stock. Considering their product description is the same as that used by Taos Herb, word for word, I would guess they both get it from the same supplier. Medicine Man and Taos Herb both have herbal blends for smoking that contain true kinnikinnik, as well as other plant materials. The Medicine Man blend appears to have red willow bark, while the Taos Herb blend does not.
There used to be an outfit that produced purportedly authentic native smoking blends in several different varieties, back in the seventies. They had a "Ceremonial Blend," a "Northwest Coast" blend, etc., and they advertized in the blackpowder shooting magazines, catering to the buckskinner/rendezvous crowd. Whoever that company was, they hung on for a long time, and may even still be in business. Their mixes were pretty coarse, though, and actually had chunks of wood in them. The botanicals I have bought from Prairie Edge and Taos Herb Company were much higher quality.
Best regards,
Notchy Bob