Kia ora!
There's a lot of us out here! The best place is Facebook these days. The two best ones are "NZ Cactus Chat" and "Cactus Buy Sell Trade New Zealand". This forum is definitely more Australian focused from what I've seen in my lurking (although I don't doubt there are kiwis in here).
If you're interested in freaky trichs that buy sell group is definitely the place to be. Here's one of my recent scores from that group, T. helen x T. olivia :D