found this today.
http://www.mutazu.com/products.php?cat_id=121&menu=Driver side backrest&product_id=279&s=prod.php
it fits the corbin post and the price seems right.
I may order one ....but prefer the oval back myself.
MaxB (who is still waiting for his corbin seat)
i did order the seat with the butt rest moved back 1 inch. So it is special order.
my typing is terrible today, sorry.