Though they like to, at least allude to, a long history and an association with the National Stringed Instrument Corp. of John Dopyera and George Beauchamp, there is as far as I can see, no actual link. National Reso-Phonic Guitars was founded in 1989 by Don Young and McGregor Gaines in a workshop, (reputedly a garage), in California. In 1990 they moved into a factory in St. Louis Obispo where they still are. 

From the start they set out to make very good copies of the old National resonator instruments and have used branding and logos to further enhance the historical connection. They also offer a full repair and restore service on any old National instruments a customer sends them, (as this helps them make sure their copies are exact).

As well as producing reproductions of some of the Guitars, Mandolins and Ukuleles that were produced by the original National, they also make quite a few new designs including a mahogany, koa or maple wood bodied resonator Ukulele model. All of the Ukuleles they make are concert scale and they have not reproduced any tricone Ukuleles, (or Mandolins - it was never that clear if the tricone Ukuleles were actually 4 string Mandolins, they certainly used the same bodies - that National Stringed instruments made). 

National make the cones for Mya-Moe and some other makers resonator Ukuleles as well as their own. 

Ukuleles disappeared from the website in 2017 and I don't think they are made now. 

One other thing to note is the wood shop part of the factory at St. Louis Obispo is a place where a number of now independent luthiers learned, or at least refined their craft.