Also, you can sell Everstones to the Gentleman in the Pokemon Center in Icirrus City. He'll give you 1,000 Pokedollars for each Everstone you sell him.
You can find Everstones easily by fighting Roggenrola in the Wellspring Cave, make sure you teach a Pokemon the move Thief (TM46) and you can steal Everstones off the Roggenrola, which hold them 50% of the time. If you're using a Gothita/Gothorita/Gothitelle it will be slightly easier thanks to their Frisk ability which makes them able to see the foe's held item.
Thank you! I'm going to get to Nimbasa to battle the trainers there. Also figured out that if you go to Driftveil Drawbridge and pick up all of the feathers all of them except for the Pretty Wing sell for 1500 each, and you manage to get 10 in a minute pretty much.