You can find an everstone hidden in the mines below the great staircase; you need to be able to use rocks smash, but you would need it if you wanted to mine anyway. Head toward where you met with the Meteor thugs, and when you go down the muddy hill with all the jump ledges, take the outlet that's second from left. Right in front of you should be a stalagmite with a breakable rock below it. Break the rock and search the stalagtite from below. Congrats on your everstone.