[Brilliant Diamond & Shining Pearl] Having no luck with sun stones

So i'm currently trying to get as much as the national dex done for BDSP and i am trying to go for the easiest ones first (dont worry about a few traded ones i have a trick for that) and currently need sunstones for a few Pokémon but i haven't found any at all which sucks.

I just hope I can get most of it done before I start Pokèmon Violet arrives (i have it pre-ordered)