It seems like every new "Pokemon" iteration in the franchise adds new evolutions for the versatile Normal-type Pokemon Eevee. While "Pokemon Sun & Moon" doesn't add new evolutions to the line (although it should) you're gonna want to know where you can find each Evolution Stone so you can get the Eeveelution you want, and other Pokemon, too.
The four basic stones, Fire, Water, Thunder, and Leaf to get Flareon, Vaporeon, Jolteon, and Leafeon can be found easily in "Pokemon Sun & Moon," according to VG 24/7. In fact, all of the Evolution Stones can be bought at the store in Konikoni City. So far, the Water and Leaf Stones can only be bought there, and can't be found anywhere else.
But if you want to find it naturally in the wild, a Fire Stone can be found at the Diglett's Tunnel over in Akala Island, and a Thunder Stone can be found at the Dream Park in the same island. Other Eevee evolutions, such as Umbreon and Espeon, need a certain level of Happiness and leveling up at the right time of day.
Meanwhile, the Ice Stone, which you'll need for Alola Ninetales or Alola Sandslash, depending on the particular version of "Pokemon Sun & Moon" that you have, can also be bought in Konikoni City. An Oval Stone, needed for a Happiny evolution to Chansey, can be found at the Paniola Ranch in Akala Island. A Dusk Stone, which you'll need in order to evolve Murkrow and Misdreavus, can be bought at the flea market at the Malie Community Center, or at the beach in Poni Wilds.
For more tips on what you should do once you fire up "Pokemon Sun & Moon," read the short walkthrough over here on GamenGuide. Good luck getting all the evolutions you need!