The New Zealand Go Society has been established for forty years and now has half a dozen active clubs in most major cities. Click here for the official NZGS website, the NZ Go Wikia, or check out these local Go clubs:

The newest formally affiliated club was in Hamilton in 2008. Here is its first press release (now rather dated, but it seems to be the latest available!):

While we are starting small we want to get big!
So everyone is welcome to come and play Go: young, old, strong, weak and beginners!
If anyone who is reading the mailing list could pass the information about the start of a Hamilton club on to anyone they know who lives in the Waikato it would be greatly appreciated.
There are a few go players in Hamilton that are attempting to start up a club. The first get together was held on Wed 2 April 2008, and had about half a dozen players turn up. At this (early) stage, we are planning on meeting once a month, and seeing if we can get critical mass for a club proper.
Venue: Vagabond, cnr Anglesea & Bryce St.
Time: 6pm, first Wednesday of each month.
Contacts: Len Trigg (021 624 595), Mike Keehan (07 843 9014), or talk to Patrick at Vagabond.