There's an ukulele store called The Ukulele Store in Koloa, not far from Poipu Beach. When I was there in 2011, it was owned by the same guy (Sam Bonnano) who owns the Kamoa store in Kapaa just as Sam was starting his Kamoa brand. Back then, both stores sold Kamakas and KoAlohas and Kanile'as. I think the Kapaa store now only sells Kamoas. The Koloa store may still sell ukuleles other than Kamoas (it was closed the Sunday I tried to visit in February). Strings and Things in Hanalei is worth a visit, too. There were a number of interesting Kauai-made ukuleles there, lots of cool old vinyl records, and stuff for all your yarn and knitting needs.