How do you find swarms in Pokemon Diamond?

Answer 1

After you beat the Elite 4 and obtain the National Dex, talk to Dawn's Sister and she will tell you the location of a pokémon from outside Sinnoh. Then go to the location and use the PokéRadar and you will be able to catch it. But the Pokémon and location change each day, so you can't catch more than one swarm Pokémon unless you have some kind of cheat...

Luckilly, I have. After you catch one swarm Pokémon, save it and then turn your DS off. Then change your DS Time to 23:59. Then turn your DS back on. Since they change each day, by the time you turn your DS back on it will say 00:00, meaning the beginning of a new day. Then you can go talk to her again. And she'll have a new Pokémon and Location for you. Hope I helped. Enjoy!

Click on the related link at the bottom of this question. The website will tell you where the swarm Pokemon are. Go to a patch of grass, use a max repel, then use the PokeRadar and look for the grass that moves. The moving grass that is brighter than the others usually has the swarm Pokemon!