How Do You Get Through The Dark Cave In Soul Silver?

I don't know I'm trying 2 do it myself and it's driving me insane!! >_< but you do need to use the move Flash (you can buy it from the Goldenrod Department Store ^.^) and: Rock smash; strength. I cannot get past the guy in Mahogany and I can't find a different exit in the dark cave buy New Bark and Violet!!!!! >_< sorry if this is long -.-