I need it to breed my Event Emboar so I can pass down its Hidden Ability. I'm going to Masuda Method for a HA Shiny Tepig.
from a Secret Pal in the Secret Base or from the following wild Pokémon;
Secret Base pals
5% chance to find one on wild geodude/gravelers and 50% on Roggenrola/Boldores
Everstones can be found in secret bases. If one of your secret pals knows the special skill "pick up stones" tell them to use it and maybe will get an everstone. i've gotten two that way!