Scuba certification is a popular subject...
You can do a search with “scuba certification kailua kona hawaii” and from that list you should see Jack’s which has been around many years, and also FairWind..
I happen to have a friend who is certified as a diver and as a ship captain right around here at the farm, I will ask if he has any particular recommendations....
Alright, he said that if you like big groups and lots of attention, Jack’s is a good choice. If you are more self starting and like small groups, Sandwich Isle http://www.sandwichisledivers.com/ would be a good fit. He also said there is a good week of study (at least 20 hours) that can probably be done at home before you come — contact a couple of these companies and find out if you can do the learning at home so you can just pass the written part when you get here. You will still have to spend at least two days on diving trips probably two trips each over two days to get all the hands on experience. If you allot for taking the knowledge test, some time spent in going to and from classes, some time to get started, you could blow through 7 days and not have any vacation left if you only come here for a week.
He also said there is now a current trend where you can go on supervised dives without getting fully certified — that is an option if you don’t have sufficient time during this trip to get fully certified. The dive shops are happy to promote this option as they obviously get paid well to supervise but it does work for those who want to dive but really can’t take the time to get certified so they can get their own tanks filled with air.
He said to start at padi.com http://www.padi.com/scuba/ and that most all resources you need should be there...