They won't sell you one. They make theirs. If you're handy you can build one with the Westy hinges that GoWesty and other Vanagon/Westy shops sell.
Another option is to talk to Michael at Expovans/MGMetalworks. He has made a few different styles of these for people.
Another homebrew option that has worked out well for a few folks is to take a custom van fold down seat and shorten it. You'll have to have it reupholstered but that way it matches your interior. Rockbender did this and his looks amazing. It's in his Chevy AWD build thread.
Currently vanless. Weird.