I would think any new zealand computer shop, especially a used parts shop, would have them. You could also look on any online new zealand supplier.
Also, I'm not 100% positive, but isn't that the same as someone else's plug? (Just googled it. It's the Australian Standard (AS/NZS 3112 (Australasian 10 A/240 V)(Type I))
It's used in Australia, New Zealand, Fiji, Tonga, Argentina, Solomon Islands, Papua New Guinea and China - that last one might be your best option for finding the right plug.