I know this response is years later but hopefully it will help another person looking....

There is a new place next to the beach in Waikiki that just opened last week called ALOHA LOCKERS on the Diamond Head side of the Moana Surfrider (next to the Police Substation) that have automated, keyless lockers for 3 different sizes. Large, to handle the full size luggage that your guests would probably need, medium for backpacks or carry on luggage, small (with USB chargers) for cell phones, keys, wallets, tablets, etc.
alohalockershawaii .com
Their hours are each day from 7 to 7 and they have an attendant there as well. The lockers are automated and keyless - you can enter your locker as often as you like. It's about time someone offered lockers in Waikiki!