I want to catch it, but how do I come up in the tower?
What Swampert said was almost right. You do get it from the man in Pewter, but the item is a rainbow wing in SS. You get the Silver wing from the director after saving the radio station from Team Rocket. The reason for confusion is the 2 items locations are swapped in the SS and HG
You have to get a silver wing from a man in Pewter city in Kanto. The man is found by following the path up to the poke-mart and going right and then going up after 10 steps. The man is old and bald.