More links and websites
The New Zealand Book council maintains a searchable database of many New Zealand authors and illustrators, and amongst these are numerous non-fiction writers.
More suggestions and sources
Calder, Alex. The settler’s plot: how stories take place in New Zealand. Auckland: Auckland University Press, 2011.
Calder, Alex. The writing of New Zealand: inventions and identities. Auckland: Reed, 1993.
Gibbons, Peter. ‘Non-fiction.’ In The Oxford history of New Zealand literature in English, edited by Terry Sturm, 21–118. 2nd ed. Auckland: Oxford University Press, 1998.