Type out a nice For Sale sign for each car, details of MOT, tax etc,along with a low price, put a phone number on it etc, of a not so local pub, with a name of somebody to ask for.
or ring the local council, and say there are cars for sale on the highway, our council tows them away and issues a fine if theyre not moved.
Oh and the council first come out and stick a nice big yellow piece of paper on the windscreen telling you and everyone else what theyre going to do.
Obviously only the owner would try to sell the car as they own it, and you may get some greif if the actual owner finds out who has caused the problem.