More suggestions and sources
Best, Elsdon. Māori religion and mythology. Wellington: Museum of New Zealand Te Papa Tongarewa, 1995.
Higgins, Rawinia, and Moorfield, John. ‘Tangihanga – death customs.’ In Ki te whaiao: an introduction to Māori culture and society. Edited by Tānia M. Ka'ai and others. Auckland: Pearson Longman, 2003, pp. 85–90.
Salmond, Anne. Hui: a study of Maori ceremonial gatherings. Wellington: A. H. and A. W. Reed, 1976.