Hi, I have seen the frustration on both the user and the builder end for finding or fabricating adaptive cycling components...and have had the joy of building a proto-type and seeing it not work out for the user. Very annoying!
Anyhow, I would like to offer my help, I have a machine shop and quite a bit of experience making bicycle frames and components and would be happy to work with riders or builders to get the stuff they need made.
In particular, the articulating front end on hand cycles for off road! built one for a well publicized rider and it became so rickety that it was a liability. The original design featured a plastic bushing and adjustable stops for how much it would twist. At the time I didn't have the ability to spend as much time as needed to really dial it in (or money...). Also, the gearing assembly for the cranks, finding a way to really set up a drive train that would be stiff enough to handle the torque.
Anyhow, I welcome any contacts from folks looking to get something more useable made.
doug