Instructions
Look for the twelve Pokeballs that all hold rare candies. These Pokeballs are scattered throughout all of Kanto. You can find these Pokeballs at Mt. Moon, Pokemon Tower, Rocket Hideout, Silph Co., Fuchsia City, Victory Road and the Lost Cave.
Buy an Action Replay for Game Boy Advance. Insert the Action Replay into your handheld device and start playing "Pokemon Leaf Green." Look for the 999x rare candies cheat and use it. After using the cheat, the extra rare candies will appear in your bag.
Trade with your friends and family who have "Leaf Green" or "Fire Red." Ask if they're willing to give you any spare rare candies. Insert a wireless adapter in both GBAs. Both players must go to the Union Room, which is located in every Pokemon Center. One player must request a trade and the other must accept it.
Get a Meowth or any other Pokemon that has the Pickup Ability. Keep the Pokemon in your party at all times. After fighting five Pokemon, check to see if the Pokemon is holding anything. It'll probably be holding a berry, but it might have a TM, Nugget, PP Up or rare candy instead.