Have you thought about making one? I have a slot together ply bed that I made. Can make a king size double including the 2+1 rear seats, or a single. The single was made so I can get my MTB in the van with me, which it does fine. One day i'll try my motorbike in there instead but haven't got around to that yet.
I don't have pics but you essentially make a narrow, single bed sized frame and rest the bed board on that and the folded over double bench