Another possibility i didnt think about at first was see if you can buy a receiver from h&r, that would be legal to build a pistol from if it was never a rifle. Same thing might be possible if you could buy one without the stock attached and then write atf for a exemption, note that it never had a stock attached. It would have to have a note from the manufacturer that a stock was never attached though, thats what mossberg does on the pistol grip combo guns.