C-150 seats, particularly pilot's seats, are getting harder and harder to come by. I have a couple of extra seats, in various states of disrepair, I'm keeping for spare parts.
Some seat parts (such as the seat back) are interchangeable right and left (on my plane, at least - C-150H). I bought a seat from Dawson Salvage once. I like their site because they provide pictures and part numbers.
http://www.aircraftpartsandsalvage....=3a&sort=3a&filter_id=1#.UfGAcW1qNhE