Airways is the only provider of ATC in NZ. In the past there have been privately run towers. Airways even provide ATC at the military / air force (if u can call it that) airfields.
Generally speaking ab-initio controllers are drafted into the regional towers, a small amount do get direct entry into Area RADAR.
You do get to choose where you are posted, but ultimately it's a combination of the companies needs, your strengths (aerodrome or aerodrome/non-radar approach) and lastly your preference. However if you want to live somewhere warmer than where you are in the UK, that shouldn't be a problem ;-)