I do not think you'll find any reputable dive operators who'll take you out there. I had the same idea until I looked into it. It seems that the idea of diving anywhere near the place where the lava flows into the sea is a very bad idea.
When the lava hits the sea water it makes acid, ( I don't remember which type) which mixes around the area, and is very damaging to dive equipment and the person in it. You would not want to get it on your skin, or in your eyes, as it really hurts! at least when I got some in my eyes above water. In addition, The vapors that are rising off the water or leathal if you happen to breath it, the water is not uniformly warm as one would think, it has VERY hot pockets, that can scald the dickens out of a diver, the water is usually very cloudy, the lava tends to have small internal explosions due to methane inside the lava igniting that will send out shrapnel pieces of rock, the new material avalanches into the ocean at irregular intervals, up to a few acres at a time and the surf... I have never seen calm on that stretch of ocean. I never found anyone who would even think taking a diver out in that area. Too much liability. I even think the National park has restrictions about boats even getting close to that area.