What if you built your own version of that? maybe use a small wheel off a childs BMX for the back and a new 29" wheel from the mountain bike world. I know its not where you wanted to go with it but it might be a start.
..........and you're wanting to motorize this ? Just askin.
Those things were inherently unstable back in the day and just the vintage buff's have kept them around. When I lived in Columbus, Ohio there was a High Wheeler's Club and many of the guys you'd see riding them wore
period clothing etc as the rode in parades etc during the holidays.
I was curious about them then and asked one of the riders about his and he was quick to tell me he had taken some hair raising spills just learning to ride it well.
Then the insurance companies claim that mile per mile of travel in the USA the bicicyle is rated the most unsafe vehicle......or the vehicle most involved in mishaps. (according to to some stuff my Insurance man was telling me when we discussed my life stye & hobbies etc on an insurance application. He already knew I rode motorcycles having sold me the insurance for that)