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You cannot duplicate master balls. You only get one handed to you. That is all you will receive.
You can get 3 master balls in soul silver and heart gold with using the 999 master ball cheat. I DO NOT know the cheat code.
You have to use an Action Replay and find a cheat code. If you Google "Action Replay" and "AR soul silver cheats" you will find everything :)
IN MY OPINON master, ultra,heavy,great,net,fast.