Hey "spearslinger22", I´ve 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, it´s 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 dont´t spear any "red moki" , it´s a codex between spearfishers not to shoot them, you will often see them in the northern part of the north island, but it´s really to easy to spear them, (they don´t 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.