Sometimes people flock to auctions for those rare or hard to find books when they could just as easily buy them on the internet.
There's a very good search engine for rare and hard to find books called the Advanced Book Exchange (ABE). They list books from all over the world including New Zealand. Very often the price will be less than what you end up paying at an auction, especially if the auction is well-attended with eager buyers interested in the very same books.
Here is the ABE link: http://www.abebooks.com/ If you'd like to limit your search to only New Zealand bookstores just click on the 'Advanced Search' option.