Etsy member GeekUnique makes a line of products called Rock Dock, which are custom iPhone/iPod docks based on real retro console parts. Pictured here is the NES controller version, which goes for $34.99.
Unfortunately, this product is really just a dock. Pressing on the buttons won't do anything, so don't get your hopes up of being able to ace a vertical shoot 'em up game with it.
There are other Rock Docks made from other consoles' controllers and NES cartridges. Check out GeekUnique's Etsy store for the full lineup.