How To Get Silver Wing In Soul Silver?

You need to beat the 7th gym. Then a man selling Ragecandybars is blocking the entrance to Blackthorn City. Go to the GoldenRod Radio Tower where a Team Rocket Grunt is blocking the staircase to the second floor. Learning from the grunt blocking the flower shop, there is a grunt underground that is giving uniforms to new recruits go underground, preferably through the north entrance (next to the tent at the north part of town). Go back to the radio tower where the grunt will let you through but before you can go, your rival blows your cover. The grunt will challenge you (2 level 24 Raticates). Keep going up until you reach the 4th floor. There you will meet the Director who is really Executive Director Petrel from Mahogany Town.

Executive Director Petrel
5 Koffings, Level 30
Weezing, Level 32

He will give you an underground key. Go to the southern part of the Underground and use the key on the locked door. WARNING, you will have to battle your rival here. After navigating through the underground correctly, you will find the real director who will give you the card key for every door in the Radio Tower. Return to the radio tower and unlock the door on the 3rd floor where you will face Proton and Ariana:

Executive Director Proton:
Golbat, Level 28
Weezing, Level 33

Executive Director Ariana:
Arbok, Level 28
Vileplume, Level 28
Murkrow, Level 33

After defeating them both take the lift up and you will have to face the leader of Team Rocket:

Executive Director Archer:
Houndour, Level 35
Koffing, Level 35
Houndoom, Level 38

After defeating Archer, the director will come in and give you the Silver Wing.

You need to finish the 7th gym. .

You get it once you beat down team Rocket in Goldenrod city's radiotower..