Question

Where do I find a Sun Stone in Sword?

Answer 1

Non-renewable
- Dusty Bowl, northwest side of giant rock bridge
- Fields of Honor, south of the entrance to Courageous Cavern

Renewable
- Pickup, starting from Level 11 and getting more common at level 81
- Random item from the Digging Duo
- Held by wild Solrock at a 5% chance

Hope I helped!

Sun Stone (Bulbapedia)

Answer 2

You can get one also in Lake of Outrage (land portion) the circle of stones produces different types of stones and the chances of you getting a sun stone.

Answer 3

The Sun Stone can be found in the Dusty Bowl in Sword and Shield.

Source