The D&G GA Forum might be a better place to pose this question, but as I was saying in
another thread recently I had a great time at a the
Kapiti Aero Club near Wellington last year.
You can't really go too far wrong wherever you go out there; the scenery is great, the skies (and indeed the roads) are uncrowded and, compared with the UK, aircraft rental is incredibly cheap.
No matter where you are planning to go in NZ you shouldn't be too far from a club.
It may or may not be worth converting your licence - see
this document at the
New Zealand CAA web site. The alternative is to fly with a local as P1 which has the benefit that you have a guide as well.
The NZ PPL requires 50 hours training. The extra is in instrument appreciation and you may have to provide evidence that you've done more than the basic stuff covered in the UK PPL before you'll be allowed to rent an aircraft. An IMC fits the bill, or you can do some training with a local instructor first. I'd recommend doing that anyway by getting some training in something we don't normally get to try in the UK; mountain or floatplane flying for example.
I'm sure you'll have a great time anyway. I'm jealous!