as far as i know, according to friends, these people are reputable and have been around a long time: http://www.kayakkauai.com/. there's also outfitterskauai.com. here's a quote from them on the nature of that trip:

"this is a very long, somewhat strenuous paddle in typically heavy seas. Don't sign up unless you are up for a good workout and maybe a challenge. While this tour is best enjoyed by people who are physically fit and have some basic paddling experience, you may join us as a first time kayaker if you consider yourself to be athletically inclined and quick to learn new sports. Of course, this trip is not for non-swimmers."

you want to be with experts on this trip.