I don't see much chat about this on our forum, but another forum I hang out on has some chatter:
GS Cycles has or at least had a complete kit in May of 2020 the. The kit was not and still is not on their website, so they just recommended contacting
[email protected] if interested.
Another user over there mentioned using a Ducati countershaft sprocket (available at any Ducati dealer) up front and for the rear sprocket they used a farming equipment (Case tractors) custom one that they had the center drilled to spec.
Those are the only snippets of advice that I've found. Most of the threads and articles I see around the internet about converting Streets to chain drives are the OP wanting to fiddle with gearing or building a scrambler. Then nobody tells him how to do it, just that belts are superior and the OP is a fool for meddling with a bike set up the way that God and H-D intended.