When do you get to catch cobalion in Pokemon Black?

Answer 1

Once you have obtained Surf (given in the story), Strength (in a house in Nimbasa city), And flash (The circular city, behind the dumpster), You can get Cobalion

First go to route 6 and navigate to the rest stop, Once there surf across the river to the right, and you will find a cave. The cave is dark so flash is needed and strength is needed to navigate past some boulders.

Edit: To actually catch Cobalion you'll need three other things. The first is a Pokemon that knows the move False Swipe (its a move that cannot kill a Pokemon - it always leaves it with at least 1HP), Lots of Pokeballs (Just normal - they're only being used as a time buyer) and two or three timer balls.

Basically, get cobalions health down to half, and then use false swipe to reduce it to 1HP. I sughested pokeballs because they're cheap - throw a dozen of them, and then throw a Timer ball. If you've wasted enought turns, the Timer ball effectively becomes a Master ball. If it fails, just throw a few more pokeballs, and try again.

Many people suggest Ultra and Dusk balls, but these are pricey.