An interesting tale which I just happened across. Monkey business in Dunedin The article is quite lengthy but, to summarise, in 1953 a pair of Bonnet Macaques were obtained by the Dunedin City Council from Wellington Zoo for their newly-built Monkey House in the Botanic Gardens (presumably one of the cages in the current aviary complex). The pair had a baby in 1954. The female died in October 1956, and soon after the remaining two animals escaped and the youngest one was hit and killed by a car. The male was recaptured and the recommendation was made to rehome him. It seems a mate was obtained instead, but by 1967 he was alone again (apparently for "at least four years") and that year he was traded to a man in Picton for some birds.
Would have been in the 1980s some time, maybe late 1970s. The last pet monkeys in NZ were a couple of macaques kept by Lady Isaac in Christchurch around then.