For licence conversion info:
http://www.caa.govt.nz/fulltext/TTMR...ition_Info.pdf
As for getting into Air Nelson, be prepared to be hit with a requirement for "50 hours recent NZ IFR time". Sometimes they do, sometimes they don't, but in any event it is an "anti-foreigner" device. They also use it to weed out Kiwis who have been so disloyal as to go to Europe and fly there for a while. How do I know? Happened to me (and others on this forum).
There are other operators, but not with Saabs (and the Saabs are being replaced with Dash 8s in any case... except you aren't allowed to call them Dash 8's, they are "Q300s").
You will find something, but only as an F/O and you may find the pay a little low.
Great country though.
Were you with Loganair then?