I'm not sure if this will ship to New Zealand, but I bought a pair of these Onite batteries on Amazon maybe a year ago. Batteries have worked great.

The product I bought was actually two batteries + wall charger, but they don't seem to be selling that for the G3 anymore. My wall charger ended up being defective and I asked if they could replace it, and Onite sent me a whole new replacement with 2 more batteries and a charger! Fantastic customer service, you can never have enough batteries haha.