Wow, I found this forum and thread by googlesearching "kona niihau". I have one of those yellow ones, bought it as new in 1995 and been riding it since! After first few years only in summer, and there's also been few summers when it sat in garage while I was too busy riding longboards.
Anyway, I've had to replace gear shifts, saddle, bar grips and rear wheel & hub, but other than that it still has it's original set up. This spring it'll get new shifts again and probably wheels as well, but that'll be about it. I was going to install a suspension fork but I changed my mind.
It was funny to read the story & history of Niihau, I had no idea. Thanks!
P.S. I just measured the seat tube from the center of the bottom bracket to the center of the top tube, and it looks like 17 inches to me. Not sure if I got it right - is there such frame size?
- Ville