The 200 Star chest down in the Chamber of Gnomes should award the Everlasting Crown Legendary item, it's a universal hat customization. You can't miss it because it's the best looking crown of all the various crown-looking hats, it's in every characters hat collection and it talks to you while you play.
If you've opened that chest and the Everlasting Crown isn't in your items and isn't waiting in a sticker pack as a gift in the Sticker Shop then you may want to contact customer support because aside from maybe Rux's Shop I can't think of any other way to acquire it.
