Any way to get this DVD in the States?
Mailorder from NZ or Oz is probably your only option at the moment. I haven't seen it on Amazon.com, or on Ebay.com either.
Maybe get in touch with a Kiwi person and see if they can help you out.
Does NZ use the US DVD format or another?
Australia and NZ are part of the Region 4 DVD code:
link
The US is Region 1.
In plain language, this means that a New Zealand DVD will not be playable in the vast majority of US DVD players. However, I have bought Region 4 DVDs from Australia and NZ and played them on my region-free player here in the US. Region-free players are easy enough to buy from Amazon.com, and don't cost the earth. I believe mine was about $60 USD or thereabouts. It was a birthday present so I could watch all the DVDs I brought from home when I moved.
My copy of "Utu" is a Region 4 DVD, and my copy of "River Queen" is a Region 2 disc, as are my copies of "Band of Brothers", "Father Ted", "Black Books", "Blackadder", "Zulu" and plenty of others. I can watch them all on the region-free player without any trouble.
The series looks very interesting. I might pick it up.