Hey "spearslinger22", Iīve been travelling all the norh Island and the south island for about a year with my girlfriend, there is really awesome diving in NZ, especilly the nort island.
So actually yes, Coromandel is really good for spearfishing,there I caught the biggest snapper in my live (was 12,8 kg), I can post a picture if you want.
Other really good places are Capiti Island, itīs in the south-west of the north island, and the hole area around there. The best spearfishing is probably white island.
If you look on a map, you will see that East Cape is amazing to dive, lots and lots of kingies around there.
If you are interested, I can describe how to access some really good places which I discovered around Whangerei, but pay attention dontīt spear any "red moki" , itīs a codex between spearfishers not to shoot them, you will often see them in the northern part of the north island, but itīs really to easy to spear them, (they donīt run away when they see you).
If you want I can give you some contact details from some spearfishing guys in NZ, they have boats and can go for a tri

p with you.