Interior panels can be purchased from Plane Plastics. They usually need a little trimming to fit perfectly, but they are reasonably priced. (as aviation parts go) Most used panels will be brittle and probably won't survive transit.
They are also a Fly-In sponsor! If you use them, please mention the 150-152 fly-in and the club. They might give a club discount, I just don't remember off the top of my head.