Well you could just pay them illegally under the table. I'm ignorant about NZs economy, and you have good points/questions but I felt that it needed to be said.
In the US we have huge migrant groups that are responsible for a large amount of the harvesting in this country, and most are paid well under minimum wage. Not saying it's right... just how it is.
Also, interesting you posted a Glenn Greenwald article - he has been accused by some people in the U.S. of dismissing things Russia has done recently in these fronts.
It's different. EU is in NATO with US (most of EU). Buying from an ally vs a non ally (or enemy depending, Ukraine for instance) is a very big difference.