It would not be hard to go nude diving at Kaloko-Honokohau National Historical Park,although it would be quite a haul a tank and dive gear out to where you would be in a secluded area. Most people park at Honokohau Marina and then walk the 10-25 minutes to get into the park itself. However, there is another entrance on the northside of the park so you can drive in and bring your tank more easily. But beware of the NPS rangers patrolling.
It has been known to have nudist (including gay cruising) but the park rangers have been ordered to crack down on nudists. Still, once you're in the water, you can always remove your swim trunks. However, the water's too shallow until far out. I think the best place might be Puako - about 30 miles north of Kailua-Kona -- it is surrrounded by private homes so public nudity would be risky, but again once you're in the water can remove your trunks and the diving there is wonderful. Puako is a long straight stretch of a two-lane road lined on both sides by luxury homes. There are quite a few small public beach access points or you can drive to end and find a larger parking area (not paved). Again it is not a nudist area, but I find a spot that is fairly deserted and take off my clothes discreetly.
It's fairly shallow out to about 75-100 meters from the shore then its starts dropping off to 20-30-40m and there is always great wildlife. I get my tanks at Kohala Divers (instead of bringing them from Kona) - the dive shop is in Kawaihae - just 4 more miles to the north of Puako.) Mauna Kea Beach (a public beach accessible from the hotel of the MKB Prince Hotel) would also be a great place for snorkelling and diving (not nudist but you can make it so - it starts our shallow (good for snorkelling too).
