If you're after central north island operators then new plymouth, hamilton and hastings are your boys and they all operate PA31s, so that would be a very useful type rating to have if you wanted to crack the ambulance market, hint hint
Couple of other words of advice before you fire off those cvs though ... have a think about what you want from aviation, if you have a wife or a family then you better make sure she understands all the implications of it, and don't even bother pursuing it if you are at all interested in a 'normal' 9-5 flying job or some sort of a family life.
Contrary to popular belief that the job is on some way glamourous, the day to day grind of the task basically consists of crap like getting called out from a deep sleep into the teeth of some august blizzard at 0230 am to fly a circling approach to minima up some high sided valley in the pissing rain to a hick east coast airport like wairoa, to retrieve some 600 lb hairy monster of a gang prospect who's not been taking his psych medication and just had living
kicked out of him in the pub. If you don't have a certain kind of mental attitude and if you aren't totally on top of your game in that environment then you are going to have a very short and sweet life expectancy. If it's just multi-hours-for-airlines you're after then there are a LOT of easier ways to get them.
Oh yeah, and have a long hard think about how you are going to react the first time you are faced with some scenario like transferring some critically injured toddler to wellington burns unit after he's just fallen into the guy fawke's bonfire. I consider myself to be a normal, hard-bastard, non-emotionally affected kind of a kiwi bloke but it really affects you in ways that you wouldn't have expected, when you can see, and hear, and smell, a baby suffering in incredible pain before your very eyes. God they smell awful, like a pork chop or something, but you know they're alive, and they are crying the most heart renderingly awful sounds you've ever heard and you've got to listen to it all the way from Gisborne to Wellington. Stuff like that - particularly when kids were involved - is probably my most abiding memories of my air ambulance days, and I can tell you they aint going to fade in a hurry.
Hours wise, I can't say for sure because we apparently have some 'pilot shortage' going on back in NZ these days
but back a couple of years ago when I was doing it, it was pretty much 1000 TT-with-some-multi as a minimum insurance requirement for a hot ship like a chieftain ... and if you come from the Hamilton area and have those kind of hours then I presume you're already on the way to Eagle
Good luck ...