L... Luthiers (21st C.)

Based in Na'alehu on the Big Island, he has been making and repairing Guitars and Ukuleles since 1969 and is authorised to do repairs for Martin Guitars. His branding is Po Mahina and the catalogue includes all scales from Soprano to Baritone plus Pineapple, Lili'u and Taropatch Ukuleles and Guitaleles. He has a couple of interestingly different Designs too, one is he makes Selmer style Tenors and Baritones with D hole or Oval sound holes he calls his Island Jazz models and the other is a Hawaiian Tenor Guitar/Giant Baritone, (and he sells it as a large body 23 inch scale Baritone too), he calls the Buddy Fo Special - and he likes to make a few Cigar Box Concerts too. As well as his own workshop he is also the house luthier for Hilo Guitars a big Hilo Ukulele shop and teaches Ukulele building at Keaola Beamer's Aloha Music Camp. 

From Vancouver, British Columbia, all of his output I have seen have been very faithful copies of 1920's Martins and he apparently even makes his own reproduction tuners.

Peter Lieberman uses the branding Maui Music. He has been making Ukuleles for over 25 years, he started out as a woodwork teacher on the mainland who also made Guitars as a hobby, then he moved to Maui. The Ukuleles come as Soprano, Concert or Tenor and are sometimes made distinctive by having an oval sound hole as a feature and sometimes a pierced headstock. He has wide distribution through shops in North America and Japan, so to service this he only makes on spec and is quite prolific. 

He was a long time employee of Martin who did a lot of the inlay work for them. He is also famous as a historian of Martins output with at least one book to his name. When he retired from Martin in about 1995 he started making Ukuleles, largely based on old Martin designs. One of the Ukuleles he is famous for, is the one he made as a think piece from green marbled Formica. He died in the mid 2000's (I have seen a couple of different dates for his death).

Ernest Loo is based in Hawaii, (I believe Honolulu) and he has been in business since at least 2011. As well as Ukuleles he makes wooden toys and says he makes Guitars, (though I've never seen one). I think there is a Facebook page which may have more information on but I can't find it? 

He was born and now works in Buenos Aires, Argentina. He has been a full time luthier since the early 2000's and makes Guitars, Cuatros and Tenor or Soprano Ukuleles using local wood. 

Bryan Luker is based in Hilo on the Big Island and brands his ukuleles Haiku. I have only seen him make Tenors.