Some of this information is a little out of date because this happened in 2004. As I didn't have much luck with finding the right sort of bike when looking on line I ended up shipping my bike over. I advise you to take a look at Trade Me (NZ equivalent to Ebay) about finding availability of used motorcycles. You won't regret an extended m/c trip there. I ended up staying 7 years and getting married to a Kiwi girl. If you are really into M/c riding the previous reply as the South Island being a spectacular place to see and visit is right on the money. But for all around riding and living the North Island is great. There is a reasonable motorcycle/car rental location in Hamilton, the centre of the North Island called Waikato Car Rental Ltd, www.WaikatoCarRentals.co.nz
ask for Murray. Tell him Bob recommended from the US. We used to do some Sunday riding with him. We are now living in the Ozarks in the US but if you have any additional questions get in touch.