air brake controller
I would start with a heavy truck shop, they might have the system you are looking for.
Another possiblity would be a truck salvage yard. Big trucks have the trailer air controlled off the normal foot brake, and also have a hand brake (sometimes called a johnny bar or johnson brake) mounted on the steering column.
Either way, you would need to plumb them through the cab. The truck dealers might know of the legality of an air braked trailer behind a vehicle without a factory air compressor.
Good luck.
Scott