You need to reach Kanto's Pewter City. Once there, talk to an old man in the town and he will give you the Rainbow Wing. I think you must beat Pewter Gym 1st. If you can't find him just talk to everyone in town.
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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.
in pewter city
You get the Rainbow Wing from a man in Pewter City next to the poke mart
You can't get them.
Those items aren't in LeafGreen.