Not in the US they aren't, since they're made by Hershey and not Nestle and so are a completely different product.

I had a coworker who would fly to SE Asia a few times a year, he'd always bring back a small suitcase of insane KitKat flavors from Tokyo airport (or nearby). One time he had a bunch of varieties of green tea KitKats, never seen anything close to that in the US.