Instructions
Travel to one of the "SoulSilver" locations where Corsolas live. They appear in Cinnabar Island, Cerulean City, Cianwood City, Olivine City and Cherrygrove City, as well as along Routes 19, 20, 21, 34, 40 and 41.
Walk around your chosen area, engaging in fights with Wild Pokemon, until a Corsola attacks you.
Capture a wild Corsola: Corsolas have an extremely low capture rate, so do not just throw a Pokeball at them. Engage it in battle to weaken it, but do not kill it. Corsolas are weak against physical attacks, ground attacks, grass attacks and electric attacks. When you have damaged it significantly, throw a Pokeball at it to attempt a capture.
Repeat the process until you've captured a Corsola.