Suggest you try the forums at crew.org.nz (either 'Marine Talk' or 'Open 8.5'). The guys there are pretty friendly and I'm sure will point you in the right direction. NZ's strongest cat classes are Paper Tiger, A Class and Hobie 16. Not sure what is going on in the Wellington region and winter is probably not the most sailing-friendly time of year in that part of the country. You should consider traveling a little to see the country anyway, so you may find better opportunities further north - e.g. Auckland or Bay of Islands.