Can only speak for Auckland, and I don't know your transport arrangements, but here's my take:
Hobbycity - Lunn Ave, East Auckland - lots of 1/72 and 1/48 Hasegawa kits at the mo, as well as Airfix/Academy/Trumpeter etc...but not that cheap, more RC-focused really, but does have a fair selection of plastic scale-modelling supplies etc..and the odd in-store specials on kits.
Modelair - just off Dominion Road, Central-ish Auckland - real deal LHS scale-modelling hobby store - retail pricing [obviously], but knowledgeable friendly staff and some good in-store-only pricing on kits, decent supplies
Stoker Models - in Greenlane - about 1km from Greenlane roundabout on State Highway One -quite diecast/car model focused, but does have a decent supply of aircraft kits - wide range of brands, and again, some good in-store pricing of kits
Modelroom - in Papakura - outer Auckland - only bought from them online, but the owner is very friendly and knowledgeable, prices seem pretty decent, but haven't set foot in the shop so cannot really say much more.
Hope this helps, PM m if you want more details?