Shellos cannot be found in Pokemon Black or White. You can only obtain Shellos through PokeTransfer or the Pokemon Dream World.
there has to be a pokemon outbreak for it to work, s/he is in route 2
Try route 222
sentret
The Route near Valley Windworks over the bridge.
You need to watch the TV for the Route that the outbreak takes place.
route 203 (mass outbreak).
The Pokemon are Chatot,Tentacool,Tentacruel,Floatzel,Gastrodon west sea,Shellos west sea, Finneon,Gayarados, Lumineon,and mr.mime
evolve shellos or route 218
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.
wait for a mass outbreak on route 207
When the electric boards say there is an outbreak of Pokemon in route 10 that is where you can get one
It is determined by the in game television it will be either Seedot or Surskit.