I have one of these in mine. Works well while the kids are small.

http://avfab.com/cessna-150-152-child-seat-auxillary

You should be able to find one on e-Bay if you keep looking. Might also want to check with the bone yards.

Eric Olson
Portland, OR
N7165F 1966 Cessna C-150F
Troutdale, OR (KTTD) Hangar C1
John 14:21