I get my xantham gum from woolworths and the other flours from commonsense organics. Bin Inn also does a good range of gluten free products.
If you don't want to make the trip you could try www.iEproduce.co.nz or http://www.commonsenseorganics.co.nz/shop/
eta: xantham and guar gum are the same thing (or do the same thing) so if you can't find it labelled as xantham just grab some guar gum
Edited by MrsMojo