In Hawaii? Rather shop in person than on the web?
Find Hamakua Hairbrushes in these fine island galleries:
Hawaii Island:
Big Island Grown Gallery, 45-3626 Mamane St, Unit C, Honokaʻa 808 775-9777
Waipio Valley Artworks, Kukuihaele (Waipi'o Valley outside of Honoka'a)
Kauai:
The Koa Store, Lihue and Koloa