Just back from NZ where did one tourist type flight in MD 500. Nice ship.
I did some fixed wing flying with Air Wakatipu out of Queenstown which were a nice outfit. I would recommend them if you want ot fixed wing touring.
As regards rotary based on farm rounding up sheep and cattle you are probably better off in Australia. From what I could see NZ heli fleet were or are either used ferrying tourists around the sights or with deer hunting/fishing down in Fjordland.
There is an operator on North Island
http://www.helinorth.co.nz that do work with forestry and agriculture but it does appear they do not use them rounding up cattle/sheep.
I know of one operation
http://www.flyinn.co.nz/ , using fixed wing, that offer touring in South Island and you get to stay on a working farm. I have a feeling they night just give you a quad and a sheepdog to gather the flock.