In reply to Gnomals:
Hi
Be aware that a lot of the outdoor shops in Christchurch (e.g. Bivouac, which has most things usually found in a UK shop, at double the price) were on Colombo street, which was right in the middle of the worst city centre damage during the Febrary earthquake. They have another store open (www.bivouac.co.nz) but I'm not sure about the others.
If your final destination is not chch, queenstown has some well equipped outdoor shops, and most south island tourist towns have at least one camping/hunting/fishing shop (sometimes incorproating DIY and hardware).
The specifically outdoor chains you want to search are
Bivouac, Mountain Designs, R&R sports, Outside sports (in the south); Kathmandu are everywhere but usually only stock their own-make stuff. MacPac also have stores but they are mostly about their own products too. There's lots of independents.
From a quick nz based internet search, a thread on another NZ hunting forum suggests Kmart (a chain of discount, erm, "department" stores), Dwights outdoors and Rebel Sports (normal sports shop).
Hope this helps - looks like you can gt them, just have to hunt around a bit.