Yakima Valley Hops has a small selection.http://www.yakimavalleyhops.com/category_s/1890.htmNikobrew sells some too, but their prices are insane.I have yet to find a store that stocks more than a handful.
I get them at farm house brewing supply.http://www.farmhousebrewingsupply.com/4-oz-bags/
But if I'm not mistaking, Galaxy hops are Australian and not from NZ.
For what it's worth, I'm a big fan of Motueka in combination with Galaxy. I tried Riwaka as well once and they were great but harder to find. I get mine from www.torontobrewing.ca but I'm guessing that there is likely someone in the US that would be easier for most of you. But if not, give them a try because they are great. I love how they show the country of origin for every hop they sell.