Who sells a single shot 410 pistol?
I believe the Thompson Contender could be found in .410. There was a company from Argentina which manufactured a single shot pistol which, by replacing the choke, could fire either a .45 Long Colt round or .410 shotgun shell. As far as I know, they're no longer in business, and you'd have to search for one which was for sale.. offhand, I'd recommend Gun Broker, Auction Arms, and Guns America. You'd have to buy it there, and have it shipped to an FFL for receiving.