We currently have three regional communities, and I don't think we have enough users for more at this point. We have !auckland@lemmy.nz, !wellington@lemmy.nz, and !southisland@lemmy.nz.
These broadly cover the country, anyone from outside these areas should just pick whatever is closest. Once we get too many posts about a certain area we can break them off into their own community. But at the moment, none of the regional communities have a problem with too many posts.
For yourself in Christchurch, check out !southisland@lemmy.nz.