NIWA maintains the national climate database for New Zealand, and can supply data in a variety of ways.
The National Climate Database is an archive of climate observations which in some places extend as far back as the 1860s. There are several ways to obtain data:
Frequent New Zealand users of detailed station data should register for free climate data access.
Virtual Climate Station Network (VCSN) data for individual points can be obtained through the NIWAData Portal
For travellers and tourists
There are also links from here to free summaries of monthly conditions at 30 New Zealand climate stations.
This gives links to information about regional climate, monthly climate summaries, and worksheets for classroom exercises.