Question

Where is the Stone Edge TM in Black/White?

=/

Answer 1

TM71 (Stone Edge) is found in the Challenger's Cave in BW, though it is only accessible through Route 9 after defeating the Elite Four and Team Plasma. Requiring Surf, though Flash makes the cave easier to traverse through. Quoting Smogon,

Traverse the entirety of the cave until you are in the deepest floor. Use Surf and immediately take the first path that diverges to the south. When encountering an opening to the west, land and jump over the ledge to claim the TM nearby.

Answer 2

Its in Challenger's Cave Which you can't access until post game.

http://pokemon.marriland.com/black_white/walkthrough/postgame/challengers_cave

That pretty much walks you step by step through the cave.