Or grow them. They fruit twice a year as far as I can tell and they keep for ages. I planted a hedge of them and give away supermarket bags full regularly. Most things taste better with some lime juice. They require zero care and at the current 35+ degrees Celsius, are borderline a requirement for living.
If limes (or anything else, like grass, or strawberries, or potatoes, or mint, ...) happen to grow on your property it's fine and you can collect them, but if you tend to them or there's evidence you planted them it's gardening, and the penalties can be steep.
And police don't look kindly on non-native tasty edibles[0] which "just happen" to grow on the properties of unlicensed owners, as often as not the owner is assumed at fault and fined (though of course the harshest penalties like prison require positive evidence of guilt).
Is there some sort of water or soil restrictions that warrant the licensing requirement?
I know NZ can be resource limited for a couple of reasons, but I'm trying to imagine why growing things would present enough danger to warrant the law being involved.
I have no idea why, but limes are extortionately expensive in New Zealand, even for imported goods.
They're currently NZ$35 per kg (over US$10 per lb).
It's standard to get a slice of lemon in your Corona (which are also extortionately expensive in NZ)