After you obtain the National Dex in Pokemon Diamond/Pearl, you can go to Pal Park, where you migrate Pokemon from a Gameboy game to your DS cartridge. So, clone a million masterballs or other items on Pokemon Ruby, Sapphire, Fire Red, Leaf Green, or Emerald, give them to pokemon, migrate the pokemon, and viola, millions of that item on Pokemon Diamond/Pearl.

Submitted by Three_Year_old_gamer (dragonboy1000), XSaleemX