It exists, I own one. It came with a GW690 I bought on eBay, seller didn't even mention it in the auction but just included it. The vented hood is made of plastic and has a metal mount that tightens with a small screw. When mounted, there's minor viewfinder blockage and you cannot use filters with a thick ring.
By the way, only the old GW690 has a separate hood, the newer models have it built in.
Try eBay if you need to purchase one. I can PM you the name of the seller I got mine from if you like.