Watsonian? I've seen a number of them but they were different. I almost bought one from a guy up north of me. I decided not to purchase it because it was a bike specific mount and found that it would be a bit of an ordeal to modify it.
Steib was still being imported a couple of years ago but I believe were classified as replicas. I believe it was Blue Moon Cycle that was selling them but a quick check of their website suggests they no longer do so.
On the forks, the guy who used to used to fabricate triple trees for DMC Sidecar to lighten the steering no longer does so. I have leading legs on mine, which works, but moving the forks tubes forward to change the trail is the best way to do it.