The Everstone can be found at:
Geosenge Town (from Scientist with a STANDING house-basically top left of PKM Center)
Route 18: from Psychic Inver (Battle: get 7-9 Super Effective moves on his Pokemon)
-wild Geodude (5% Everstone held)
-wild Graveler (5% Everstone held)
-wild Roggenrola (50% Everstone held, or 5% Hard Stone held)
-wild Boldore (50% Everstone held, or 5% Hard Stone held-NOTICE-BW and BW2 exclusives)
If you want to get an Everstone easily, I suggest you catch some Roggenrola, or get the one from Geosenge Town. The rest are quite rare.