For those who don't know, Hilo Guitar was bought by someone else. He slightly changed the name of the place. It was Hilo Guitar and Ukulele. Now it's called Hilo Ukulele and Guitar, as the seller didn't want the buyer to use the same name. They have nowhere near the stuff that the original store had.
Here is a couple of music stores in Hilo.
http://www.bigislandguitars.com/
The other is Music Exchange at:
792 Piilani St.
Hilo, Hawaii 96720
(808) 961-3363
Maybe have your friend call ahead and ask if they stock harmonicas.
I envy your friend because he plays such a compact instrument. I started off playing drums, and switched to guitar. I'm a hack. I started playing the "penny whistle", or tin whistle, and the fife, and recorder maybe a year ago, just as a hobby. Amazing what can be played with the tin whistle with only six fingering holes.
I'm getting back into guitar after having not even touched one in maybe 3-4 years. Building up new finger callouses now.
Jon in Keaau/HPP