Pokemon Soul Silver Cheats :
Secret - Masterball-
I think there are only three ways to get a Masterball (without cheats).
1. Receive one from the Professor.
2. Trade one from another Pokemon Game (have a pokemon hold a Masterball during trade).
3. Go to the Goldenrod City Radio Tower and play the Pokemon Lottery Corner everyday. If the ID number of your Pokemon matches the Lotto number then you get a free Masterball. It's rare to get the numbers to match though. The more Pokemon you catch the more likely you'll get a matching number.