I believe you can import a single one. But as of now, in NA, it's only gonna be bundled. That's surely to change, though. It's happened before with bundled amiibo (eg: Green Yarn Yoshi, Super Mario Mario, Isabelle, etc.)
Yeah I'm certain they'll sell it stand alone eventually. The game is being sold digitially on the eShop in addition to the boxed bundle, so it'd be nonsense if they didn't have any intention of selling the amiibo later for digital owners. (hell, that's even the version I got from Nintendo for review) Plus, it's supposed to be usable in the new Zelda game later this year so they might release it for that purpose.