from a blue old guy in pewter city
You must defeat Archer of Team Rocket in the Radio Tower to get the Silver Wing.
you go to pewter city and find the old man on a hill and he will give you the silver wing
But if you get the silver wing, you just cant go to whirl islands and find Lugia. You have to get a diffrent feather. You can figure that out on your own.
You get Silver wing After defeating the team rocket in the radio tower POKEMON SILVER ONLY. Rainbow wing Is found much later in the game After the Elite four In pewter City POKEMON SILVER ONLY.
you can get lugia in the wirl islands after you get the silver wing
you get it after defeating team rocket in goldenrod lance gives it to you
you go to viridian city in kanto and talk to this old man on a hill and he will give you the silver wing
After you beat Pokemon league and you have acces to Kanto go to Pewter city. There you find an old man. He will give you (silver wing in heart gold, rainbow wing in soul silver). With silver wing you'll have acces to B3F at Whirl islands.
first you have to get the silver wing and go to whirl islands and there you will meet lugia
The head of the radio tower gives it to you...
go to pewter city, then there is a man you get the silver wing
go to whirl islands and find lugia deep inside