The Primary Sources
Researching the New Zealand Wars is so much easier these days because important primary source material is being posted on line.
Māori Census data
Here is a good example : the 1874 Māori Census returns. This was the first official census ever undertaken to count the Māori population. It was only possible because the wars had finished in 1872. However, it’s interesting because it reveals the state of Māori after the wars, though do be aware, the data was largely based on estimates (hence the title ‘Approximate Census .. ‘)
The reference for this source is: ‘Approximate Census of the Māori Population’, Appendices of the House of Representatives, 1874, G.-7, pp. 1-20.
Some of the issues / problems in dealing with census data as a primary source are discussed in a journal article written by Danny in 1995 entitled ‘Incontravertible Fact, Nothwithstanding Estimates : Maori People Observed in the Early Contact Period‘. This article appreared in Ke Pukenga Korero, Koanga (Spring), 1995, Vol.1, pp. 54-64. He Pukenga Korero is the journal published by Māori Studies, Massey University.
Land Confiscations
Alternatively, you can directly access the legislation that gave rise to the iniquitous confiscations of Māori land after 1863 : the New Zealand Settlements Act 1863. This legislation was enacted on 3 December 1863 and, originally aimed at Waikato Māori, eventually extended across significant portions of the North Island – see Map of Confiscations, which appears on the awesome Te Ara website.