Hello... bit of a long shot, but you know how it is, you've got to ask! I thought maybe someone had modified a lowlight and might happen to have a pair of seats for a 1956 karmann ghia.
These seats are known as "thinbacks" and, you guessed it, have a thinner back than the later seats.
http://images.thesamba.com/vw/gallery/pix/312278.jpgI have two pairs of 57 on front seats to sell / swap once I find them!
If you or anyone you know can help please get in touch
Cheers
Matt