[Thumper & Buttercup]

I think they people you need to talk to are the people that do this for cars and trucks. Try a search for Handicap controls.

Here is one link that came up with that search but there were many more that came up.

Handicap Hand Controls - Handicap Vehicle Hand Controls for Handicapped Drivers

Handicap Vehicle Specialists Hand Controls

Hand Controls | Hand Control | Hand Control Driving Aid | Handicap Van Hand Controls