I want to evolve my female Snorunt into a Froslass, but I can't find a dawn stone. Where can I find one?
The only way to get a Dawn Stone is in the post-game, in Hau'oli City. However, it is possible for your boxed Pokémon to find a Dawn Stones in the Poké Pelago.
On Isle Aphun, at Rank 1, it is possible to receive Dawn Stones from Path for Brilliant - Stone Hunting!
At Rank 2, it is possible to receive Dawn Stones from Path for Interesting - Item Hunting!