Home cockpit hardware - how are we supposed to do this if we don't have a complete key list?

I know I can assign keys but what if the thing I am looking for is not there.
That is what I was trying to describe. There is no AP1 & AP2 only turn on/off Autopilot - and it only does it to AP1. The same with the other examples I gave. Sorry if that was not clear.
So just to stress - I need to know how I can add keys to input that currently only seems to be able to work via mouse input.