Answer 1

To Obtain Sawk in Pokemon Black, you have to go to these Routes:

Pinwheel Forest(Outside)
Route 10
Route 15
Route 18

Hope This Helps...

Answer 2

To get a Sawk you can go to the outside of pinwheel forest, route 10, route 15 and route 18. Also, since you have black you have a better chance of finding them instead of Throh.

hope this helps :)