There are several brands of gas available in New Zealand. The main one that I use is Kovea. This comes in two types, both are resealable. One looks like a fly spray can without the plastic atomiser bit, and the other is the short squat kind.
If you want cheap gas, (the fly spray type) this is available from The Warehouse for about $2.99 a can (approx 1 pound?).
Kovea and Doite brands are available from most good outdoor stores.