Have you applied to Births, Deaths & Marriages for your original birth certificate? That's the one that shows your birth parents, not your adoptive ones. http://www.dia.govt.nz/diawebsite.nsf/wpg_URL/Services-Birth...

Do you have any idea what part of the country your birth parents lived in at the time you were born? It was likely to not be where you were born, as your mother could well have been sent elsewhere for that.

Ancestry.com has electoral rolls up to 1981, you should look for your birth parents there. That will give you some idea where they might be living now, if they are still alive.

Your birth mother may have married since you were born. Check the marriages microfiche (see if your local library or genealogy group hold them), as the online indexes don't go that far forward.

If either of your birth parents are still alive, you may be able to find them in the phone book. http://whitepages.co.nz/

Consider using a go-between for making that first contact with your birth parents. It's a very traumatic time for everyone concerned, and it may help to have an advocate helping you. Talk to the Salvation Army or Jigsaw about that.

Hope this helps. :-)

Kind Regards,
Wendy