I just ordered these devices from a German company. They are an almost perfect solution.
https://doepfer.de/we.htm
Each unit has 4 controller inputs. I purchased 3 units. Two to use giving me 8 controllers from the motorcycle - and a spare to carry. It’ll run off of 12 v - I plan to use MIDI to USB cables to plug these directly into a computer.
This is how I’ll physically be able to get MIDI generated by using the motorcycle controls…One more step figured out…It will take a LONG time to get these, so not before July - but I can get everything else ready while I wait.
Its snowing where I live - and all I need is a warm day to finish painting the bike…sigh…delayed by a month now waiting for the weather to break…