Sometimes it pays to know when to ask a professional genealogy searcher to help. This might be for adoption purposes and you've had too many doors shut in your face. It might be because you lack the experience to take your research to the next interesting level. Or you might be rich enough to sit back and let someone else do the searching.
Whatever the reason, paying for research is a very good idea. I know many people who have done this, its not a failure on your part.
Cyndi's List is a good place for references to do with New Zealand research. On her pages she lists the professional researchers who have let her facility know they are available.
Apart from this list, the New Zealand Society of Genealogists will know of others. If you are in Auckland, give them a ring.
The only professional person I know who does this is Peter Nash. Peter is easy to get on with and very knowledgeable.