Don't think there are real serious detailers out on Maui. Just those looking to make a little extra money on the side. If he's really serious about getting a good quality detail please PM me with info. I regularly fly to Kauai from Oahu every other week to take care of a handful clients out there. I'll do the same for any island if it's...well you know...worth the trip.
But if he's looking for supplies locally then YES! PakShak.com is the place. Ranney doesn't fly outer island to detail I think.