Where can you get a gold bottle cap?

Question

Hyper Training!

Answer 1

Festival Plaza lottery stalls, Poké Pelago (Isle Aphun - Rare-Treasure Hunting), Pokémon Sun and Moon Guide Book Gold Bottle Cap (Japanese event)

source

Comments

I just wanna add that for the lottery stalls to have Gold Bottle Caps as the first prize the lottery stall you're using must be called Treasure Hunt.