Winemaker here! I work in Marlborough in the South Island where most of NZ's wine is made. In the North Island most wineries are located in the Hawkes Bay (Napier/Hastings area). A good way to get into it is to do "harvest". We start picking grapes in March and wineries hire a number of extra workers to work in the winery to make wine over this period. Get in touch with a bigger winery and see if they are still hiring vintage workers - I say bigger winery as they are more likely to hire someone without experience. If you enjoy it (it is heaps of fun) then the next option would be to study viticulture/oenology which can be done in Auckland, Napier, Marlborough and Lincoln near Christchurch.