Synlait have imported a load of butter from the US, and are selling it via PNS at a good price ($6.19 is the lowest I have found at Papakura), but $6.99 at other PNS stores
Check out GroSave for PNS stores near you.
According to the NZ Herald, it is North Island this week, and making it to the South Island next week.

There were discussions on reddit about this, apparently USA butter is terrible.