Instructions
Travel to the Safari Zone and look for Dusclops in the Mountain Region. You must add 18 blocks of Forest Objects to the Mountain Region of the Safari Zone to get Dusclops to appear. These objects are obtained from the Safari Zone owner, Baobo.
Throw Safari Balls at Dusclops when you encounter it in the Safari Zone. You cannot battle the Pokemon in the Safari Zone to make them weaker, so you will likely need to throw several balls before you successfully capture a Dusclops.
Pick up the Reaper Cloth on the first floor of Mt. Silver. Open your menu and give the Reaper Cloth to Dusclops as a hold item.
Visit a Pokemon Center to conduct a trade via Wi-Fi or a DS to DS connection. You must have a friend who is willing to conduct the trade and then trade your Pokemon back to you immediately after. Trade your Dusclops with the Reaper Cloth to your friend.
Transfer the Dusclops from your friend's game back to your game to complete the evolution. When Dusclops returns it will evolve into a Dusknoir.