...Ok, I know a cheating way to get A LOT of Master Balls. Buy an Action Replay DS, download some codes from your computer, and then insert it into your DS, then when it says, "insert a game", insert your Diamond/Pearl game. Then, you can go down the list, and there should be something that says x999 Master Balls in bag. There is also something for x999 Rare Candies. Then, touch Start on your touch screen, and... voila! You'll notice that you'll have x999 Master Balls. This is the way I know. Maybe other people have different ways.