Try a flower called the Mallow flower it closely resembles the hibiscus, but the blooms get huge. They come in white with pink and burgandy centers they are lovely and hearty (just water them.) Also, try looking at different hibiscus plants they can be found in tree forms and shrub forms. They come in all colors, just remember in doing a Hawaiian garden you're going to be using tropicals. That means lots of water, lots of sun, and they dislike the cold. If you get freezing temps, you can cover them through light frosts, but I would bring them inside at least a garage for hard long freezes. They will come back if properly winterized.
Rose Mallow Seed
http://www.americanmeadows.com/WildflowerSeeds/Species/RoseMallowseeds.aspx
Hibiscus Seed
http://www.burpee.com/category/perennial+flowers/hibiscus.do
