Where is the dusk stone in mystery dungeon?

The Dusk Stone is not found in any Pokemon Mystery Dungeon game. It is a stone used in the main Pokemon series games for evolution. It is used to evolve certain Pokemon, such as Murkrow into Honchkrow.

Are you perhaps thinking of a different item in the Pokemon Mystery Dungeon games? If you tell me what you're looking for, I can try to help you find it!