You need to watch the TV for the Route that the outbreak takes place.
You have to wait until Lickitongue is your mass outbreak: Go to sandgem town (the 2nd town you go to) walk straight down from the Pokemon center, go to the bigger house Talk to the little girl and every day she will tell you what route you can find the Pokemon that has a mass outbreak
The 'mass outbreak' is a swarm of Pokemon that you would not normally find anywhere else, and are at extremely high frequency rates. You can listen to Professor Oak's talk show for what the mass outbreak of Pokemon is and on what route it is on.
You have to become the champion first.Then go to Rowan's assistant's house and talk to his/her sister and she will tell about a mass outbreak everyday.
route 203 (mass outbreak).
the places vary. check the radio to find out which Pokemon is appearing where.
wait for a mass outbreak on route 207
there is no mass outbreak girl in soulsilver or heartgold. That was in pearl diamond and platinum versions. in heart gold and sould silver the mass outbreak is found by listening to Professor Oak's Pokémon Talk on the Pokégear radio in HeartGold and SoulSilver.
rare Pokemon
its an outbreak of pokeemon from other regions
route 27 water surface mass outbreak
If you go to the town right next to your home town there is a house with a sign next to it. Below where Prof. Rowan's lab is. (The sign says either Dawn or Lucas' house depending if you are a girl or boy). You walk in the house and there is a little kid. (Same gender as you). And they tell you what route has the mass outbreak, what Pokemon are there, and that they want you to do better than their sibling.
mass outbreak