Matt, I am not flying at the moment due to health issues, will be joining Radio Control Model Planes Marlborough as soon as I am feeling better.
http://rcplanes.x10host.com/locationp.htm
I used to buy my foam from Uncle Ben's in Wellington which sell's the Readi Board foam. Started off buying the Jassard foam board from Bunnings but it was too heavy. I am halfway through a balsa/foam build of a Royal F4u Corsair 1/8 th scale. I now buy sheets of insulation foam from Bunnings and cut my own sheets with a foam cutter that I have build. Much cheaper and I can cut the foam at almost any thickness.