Ask around and it should be easy to get recommendations for good sites to solo dive in Kona. Most of my solo dives aren't because I particularly desire to solo, but instead are simply because I step out on the lanai, look at the ocean conditions and say "Wow, nice looking day! Time for a dive!" On a typical unplanned dive like that, I'll be in the water 30 minutes after deciding to go. Having to make prior arrangements to hook up with a buddy would be too limiting for everyday diving.
I don't bother with a pony for my solo dives, where most of the time is spent at 45' or shallower. IMO, at the sites I dive, the added risk during surf entry/exit outweighs the possible advantage of having a pony or doubles on dives within the range of CESA (no gas swimming ascent).
Much as awap describes, I usually solo only in familiar spots, or exploring relatively benign new spots.