Early Game:
* Route 207: You have a chance to find Shiny Stones in the tall grass of Route 207, located to the west of Hearthome City.
* Eterna Forest: Shiny Stones can be found in the grass of Eterna Forest, which connects Hearthome City to Pastoria City.
Late Game:
* Grand Underground: The most consistent way to find Shiny Stones is by digging for them in the Grand Underground. Shiny Stones can be found in different areas of the Grand Underground, but you'll need the Mining Technique to dig them up.
* Treasure Hunt: You can also find Shiny Stones as rewards for completing Treasure Hunts in the Grand Underground.
* Rarely, you may also find them as a reward for defeating a trainer.
Important Note: Finding Shiny Stones in the Grand Underground is the most common way to obtain them. You can use the Digging Technique or simply walk around in the Grand Underground and look for them. It's a good idea to visit the Grand Underground often, as it's the best place to find Shiny Stones in Pokémon Diamond.
Remember that Shiny Stones are relatively rare, so you may have to search for a while to find them. Good luck on your hunt!