Instructions
The Item Cloning Method
Turn on your Pokemon Gold game on and walk to a Pokemon Center.
Walk to a PC in the Pokemon Center.
Go into your Menu and have a Pokemon in your party hold a Master Ball. Save the game before going on to the next step, as this method can sometimes, though rarely, cause issues in your saved game.
Access the PC and store the Pokemon holding the Master Ball in a slot in the PC.
Change to a different box in the PC. The game will tell you it is saving and not to turn off the GameBoy. Ignore this message and turn off the GameBoy.
Turn the game back on. If the cheat was done correctly, the Pokemon you stored will be in the PC and also in your party. Both will be holding Master Balls.
Repeat the step as many times as necessary -- 99 times, if needed.
SS Aqua Method
Beat the League and let the credits roll.
Visit Professor Elm when he calls you and get the SS Ticket from him.
Go to Olivine City and get on the Fast Ship SS Aqua.
Check all of dustbins on the ship. They will say they are empty.
When you get to Kanto, check your inventory. If the trick has been done correctly, you should have unlimited Master Balls.