Hi Shagen,
Pick up a copy of the Lonely Planet or Rough Guide to New Zealand - most of the campsites in every area are listed in each section, and it also gives a guide to how many cabins they have available and the prices. We used the Rough Guide when we were here last, and the Lonely Planet this time and they were both good.
In fact, the Lonely Planet lives in the glove box of my car - very useful if you want info about an area you're visiting or travelling through, or want ideas of where to visit while you're there etc. It's got maps of the areas too which always come in handy!
Cheers,
Jodie