If you want to evolve your Murkrow or Misdreavus into Honchkrow and Mismagius, you’ll need to find a Dusk Stone to force their evolutions in Pokémon Brilliant Diamond and Shining Pearl.
There isn’t a simple way to get the Dusk Stone, since one of its sources requires a Pokémon with the Pickup ability. There are a plethora of Pokémon in the Sinnoh and National Pokédex that can have the ability, but one of the easiest ones to find in the game is a Pachirisu. They appear in quite a few areas and can be found early on in the game.
Pachirisu can be found on Route 205, at Valley Windworks, Fuego Ironworks, and in the Grand Underground. To check if it has the Pickup ability, head to the Summary screen.
The ability is described as having “a 10 percent chance of finding and holding an item after battle. Will not work if this Pokémon is already holding an item,” according to serebii.net. You can also find the Dusk Stone on Victory Road, the Galactic Warehouse, and the Wayward cave, but Pickup is a passive way to find it. This method can be a less frustrating way to obtain one if you’re not in a rush to get the item.
The last way to get the Dusk Stone is to wait until you have access to the Battle Tower and rack up enough points to buy one there.