However, you can get an Everstone in Pokemon Platinum by:
* Trading with a player who has an Everstone.
* Finding one in the Grand Underground. Everstones are one of the rare items that can be found by digging in the Grand Underground.
* Defeating a trainer who uses one. There's a chance some trainers may be carrying Everstones.
Unfortunately, if you're playing Diamond, you won't be able to obtain an Everstone without trading from another game.