Upload & Sell: Off
The I'iwi, Apapane and Amakihi, (little green guy*), can be found on Maui but seem to be at higher levels. Hosmer Grove campground is a pretty accessible place to find them. It is in Haleakala National Park. There is a walking trail through the grove and they can be there especially when the O'hio trees are in blossom. Walking in the area is restricted to the established trails and the park Rangers patrol the area. Leaving the trails is prohibited to preserve the grasses and foliage. You will do best with something like 400mm or better reach although you can get close if the bushes with the yellow bell like blooms are in season as they feed from the blossoms.
The Park Rangers guide walking tours in the area a couple of times a week although not completely dedicated to birds, you can phone them or details may be on their site. I have had some success but my reach is a bit marginal.
* There is a small green bird that can be mistaken for the Amakihi that is pretty widespread called the Japanese White-Eye. It is not popular with the Park Rangers as it is an introduced bird that is elbowing its way into the Hawaiian habitat. Small green but with a white ring around the eyes.