Where can you find an Ice stone in Pokemon X&Y?
Solution 1:
If you are looking for the method of evolving Eevee into Glaceon, you are looking for the Ice Rock. The Ice Stone was not introduced until Sun and Moon as a means of evolving Alolan Sandshrew into Alolan Sandslash and Alolan Vulpix into Alolan Ninetales. These Pokemon are not available in Pokemon X or Pokemon Y, and neither is the Ice Stone.
The Ice Rock in Pokemon X&Y can be found within the Frost Cavern north of Dendemille Town. You will need Surf to access the Ice Rock.