how can i get beldum

If the girl says he has a mass outbreak, it will be on route 228. There is no way to predict when the mass outbreak will occur, so you just have to wait.

All you can do is go to the little girl each day and ask, or alternately look on some TV's they will both give you the same information. What she says is completely random, I asked her everyday for like 3 months before swinubs finally swarmed. For a useful Pokemon like beldum it might be rare but stay patient. As a side note when beldums are swarming, it is in a place with a constant sandstorm, they are about level 53 and they are hard as anything to catch so be ready.

I have a good cheat. It worked for me and it only took me an hour to get all the Pokemon that you can catch in swarms. First of al you set your DS clock to 23:59. The console automatically turns off when you set the clock. Turn it back on and quickly log on to diamond or pearl before the clock turns midnight. When it does, it's a new day and you can talk to lucas or dawns little sister in sandgem town. You can do this as many times as you want and you can set your DS back to normal when your done!. WARNING! You still have to save the game before you turn it off or reset the time again!

It's THE hardest Pokemon to catch. I saved my masterball.

This is terribly awesome from Nizamur rahman