If any New Zealand Kobo users are looking for one, I've used a DSE (Dick Smith) Digitor USB charger, it does 5v, 500ma and seems to work ok.
http://www.dse.co.nz/dse.shop/en/product/M9946 The website data indicates it is a 5v 700ma charger, but it's 500ma according to the sticker on the charger itself.
Cheers,
G