If you Google "Don Stith Hawken" you'll find one source. "The Hawken Shop" and "Track of the Wolf" are other sources.

I got a Hawken kit from Don early last year. Don was in poor health at the time, so there was some delay in getting all the parts together (along with the Wuhan supply chain disruptions). The Stith kit is an exact pattern of the (a) original Carson Hawken in New Mexico and has excellent components.

I'm not sure if you've ever built a muzzle loader before, but a Hawken may not be the best choice for a first effort; it's actually a somewhat complicated design.