Not widespread since its essentially not a full martial art, its been sold that way by the german website. You can check Col Amant Pooksrisuk dvds at www.ancientmuay.com and www.bareknucklemuay.com, Col Amnat teaches the vital elements of it and possibly as a subset.
Best person for the thai martial arts in America is Vincent Giordano. You cannot ever go wrong with his instruction or insight.