Don't know if you have checked out the AW page (American Whitewater - HI State Rivers
Maybe try contacting the people who posted the photos and comments.
Most of the creek runs there have only been first d'ed within the last few years and whitewater boaters may be hard to find on the islands.
Also might want to look into getting a fiberglass surf kayak for the epic surf to be had.
On a side note...check out some schools down in New Zealand, just got back from studying abroad there. Similar terrain, year round whitewater, EPIC creeking, student visas are really easy to get, and it costs about half as much as out of state tuition in the US