In recent years there has been a concerted effort to repatriate the preserved heads of Maori to New Zealand. On top of earlier successes in Australia and Argentina, there has been a rush during 2007 and 2008 (eg see Rouen, Aberdeen, Glasgow, Chicago). Although the issue can at times be beaten up that this brutal trade was all the European's doing, you can see from these articles published in 1820 and 1831 that the trade was deplored by the governments (and at least some citizens), and outlawed when it could no longer be ignored or put down to the occasional aberration.
The NSW governor's order reproduced below (Source: Asiatic Journal. Calcutta. October 1831.) also made room to state that efforts will be taken to confiscate and return the remains to relatives. The guilty parties were individuals of both races.
This particular article and ban is in direct response to glut on the market brought about by events that began off Kapiti Island: A raid by the Ngati Toa, Ngati Raukawa and others led by Te Rauparaha on the Ngai Tahu people. (Te Rauparaha was the composer of the famous Ka Mate haka and reputedly a regular punter at the Thistle Inn, which still stands, though a recent aggressive refurbishment, insisted on by the WCC, has resulted in a loss of atmosphere for me - though I can regretfully understand why it was needed).
Te Rauparaha was a raider during the late 1820s. He and supporters had been forced from their northern homeland in the Western Waikato region, and he became a significant warlord. In 1827-28 he raided Ngai Tahu land around the Banks Peninsula area and Kaiapoi. His forces were soundly defeated, and he pondered revenge from his stronghold at Kapiti. It didn't take long to organise. In 1830 he hired (or commandeered) a brig commanded by trader John Stewart, and took it to raid Ngai Tahu once more. He was more successful this time, and came back with hostages (among them the chief Te Maiharanui (or Tama-i-hara-nui) who was reputedly tortured by Ngati Toa women, killed and eaten back in Otaki). A fair amount of heads were taken to Sydney to trade. (This wasn't the only source of heads though: a good trade had been going on in the Bay of Islands, Hokianga, and the Thames district also before this).
Stewart got in a lot of trouble over this episode, and several Ngai Tahu travelled to Sydney to testify the case. In the end though, the court said it had no jurisdiction over crimes committed in foreign countries, so nothing came of it. Ngai Tahu of the Banks Peninsula regions wanted very little to do with British citizens after that, which is perhaps why there is such a French presence down that way.
A series of further raids conducted by Ngai Tahu and Ngati Toa against each other resulted in more of these nasty goods crowding the market, which, on top of the previous atrocities, led to the proclamation in Sydney banning the trade.
Ngai Tahu in the end got the upper hand in this war, and peace was made between the two tribes in 1839, and marriages arranged. Perhaps the obligations of utu got a bit too hard follow, perhaps the Treaty of Waitangi signings had something to do with it: Te Rauparaha and several Ngai Tahu chiefs ended up signing it in 1840 and the years immediately following. Mostly though, Te Rauparaha and his small confederation had no real hope of occupying lands taken, and Ngai Tahu had so much they didn't really need that little bit around Cook Strait that Ngati Toa held.
The Ngai Tahu accent pronounces "NG" as a "K" sound. The word "Kai" in Maori means "food". I can just imagine the chuckles on board the Ngati Toa waka taua as the warriors made jokes about the "Kai Tahu"!
There is a famous picture, taken in the 1890s (I think) of Horatio Gordon Robley with a collection of heads. Be warned: it's pretty gross, and distressing to relatives.