Fire, Water, Thunder and Leaf Stone:
>One of the ways is to go underwater and find colored shards. The matching shard will give you a stone of the respective color from the treasure hunter on Route 124.
Also,
- Fire Stone: Route 123, Fiery Path
- Leaf Stone: Route 119, Route 124
Dawn Stone: Wally gives you one after you defeat him on Victory Road.
Dusk Stone: Super Training, the Aegislash balloon.
Shiny Stone:
>Shiny Stones can be found through the "An Opening of Lightning-Quick Attacks!" round of Super Training at random. This round is open to those Pokemon with 510 EVs.
... And on Route 121.
Moon Stone: Meteor Falls
Oval Stone: The only one I couldn't find. Will add later.
Sun Stone: Mossdeep City
All of these can also be obtained through Super Training, so you pretty much have an unlimited supply of these stones.
Sources: 1|2
Hope I helped!
