jumpseat/child's seat?

does anyone have any information on the availability of the child's jumpseat 
that was once offered as an option on (at least) the early sprites? i'm 
talking about the small seat back and cushion that were mounted between the 
two regular seats and sat on the drive tunnel...if none for sale, how about 
pics, dimensions, frames, anything? any and all information is appreciated. 
thanks.

doug k.