at lake valor go inside every house he might be here
Surf is HM #3. :-)
you get from alder at twist mountain.
Get the HM Surf then teach it to a pokemon.
You get HM Surf and surf there
one of the gym leaders give you it
you need to find the hm for surf but you can only use it when you beat the gym leader pryce.
You need a water Pokemon and the surf HM
You can get surf in Pokemon black and white by battling Cheren at the Twisted Mountain. Then Champion Alder will give both you can Cheren th HM Surf.
In the safari zone at fuchsia city.
You find it in the Giant Chasm. You need the HM Surf to get there.
U can find the hm Surf in the solar cave at the 20th floor, u don't have to need a key, but u've to need a pokémon that flies over the ground or a water pokémon to take the item, bcz the hm surf is surrounder by water.
Surf is a HM so you can teach it to multiple pokemon.