Where's NZ? Through Disneyland, left at Mickey Mouse, then start swimming...;-)
There are very few trad songs, by the strict definition, from NZ. There are British songs that have a NZ version, a couple of sea songs that have no known author, and there are songs whose origins we know, including some rather good ones.
I'm sure Little Robyn will come in with a definitive list if you ask her nicely.