AmazonJosh posted on Reddit that they have a large stock of palutena amiibos and they shouldn't sell out until about 15 minutes after release. He says he's confident that they're not going to be like Robin or Lucina and disappear instantly. So as long as you are there at the right time, you should have no problem getting one :]
https://www.reddit.com/r/amiibo/comments/3d8pmu/714_amazon_megathread/ct36qdw