I have a nut wrench for smooth nuts and works awesome. It doesn't even scratch the smooth nut.

Someone is bound to still make them.

If I lived in the USA I'd be getting all my barrel nuts and recoil lugs from NSS. But I'm in Canada so things are pretty shitty now. Used to get the castellated barrel nuts from Brownells, same as recoil lugs and top bolt release sears. Now they got nothing.