Okay, assuming you have already defeated the kimono girls at ecruteak dance theatre here's what you do.
As you probably know, the raindbow wing enables you to catch Ho-Oh (the legendary mascot Pokemon for heart gold). First of all, make sure you have a good variety of fairly strong Pokemon in your party, Ho-Oh is at lvl 45 when you encounter it. Take a lot of Ultra Balls (it took me 10 to catch Ho-Oh) you might also want some repels as their are a lot of annoying Pokemon like Rattata.
Go to Barrier station and up the stairs on the left until you are on bellchime trail. Follow it until you reach Bell Tower. Get to the top via, various ladders and paths. It can be quite confusing at times, so make sure you have an escape rope. Once you're at the top Ho-Oh and the Kimono Girls will be there. Ho-Oh is Fire and Flying type so weaken it with water first then maybe use a flying Pokemon, whatever you do, do not waste your master ball on this Pokemon as you may need it later (to catch mewtwo, lvl 70, the legendary birds, lvl50, or Lugia, which is caught at lvl 70.) Make sure you save before you battle ho-oh because if you kill it, you need to be able to go back and catch it. Ho-Oh is well worth the climbing bell tower and the battle as it is an essential Pokemon, that you'll be thankful for in later battles.
Hope this helped :D
You first have to beat team rocket, then the Kimono girls
go t the radio tower and save the manager
after you defeat team rocket in goldenrod city the radio tower director will give you the rainbow wing after beating all executives.
you have to get the rainbow wing on soul silver and tidal bell on heart gold :-)
You use the Rainbow wing in the bell tower to get up to the top to battle Ho-Oh. You won't have to get it out of your item slot because your character will automatically do pull the Rainbow wing out.
you have to beat team rocket then the director gives you the rainbow wing
in goldenrod city
After you save the radio tower in goldenrod city a man comes in and gives you the rainbow wing as a reward.
in golden rod city
After you beat the last team rocket executive on the observation deck, in the radio tower in goldenrod city, you get the rainbow wing from the Rainbow wing from the director.
Once you get to pewter city a man somewhere in the city outside will give you the rainbow wing (how easy).
If you're using heartgold, after beating the Pokemon league go to pewter city and an old man on a hill will give you the rainbow wing in soulsilver and the silver wing in heartgold.
you show him the rainbow wing
Rainbow Wing and Clear Bell
You first have to beat team rocket, then the Kimono girls
you get the rainbow wing from the president in the radio tower along the lines of the story
Get the rainbow wing from the radio tower's director and then go to pro.Elm.