you must get all the badges 32 badges and beet all the champions and all the elite four then you can find registeel in the grass and regice on the ice map and regirock on the rock map I found regirock it make take long you can find suicune on the water map and raikou on the electric map and entei on the fire map and articuno on the ice map like regice you can find more ledgendaries to like lugia ho-oh kyogre groudon and more
by the mountain
You can't find registeel in Pokemon HeartGold.
it's at the place where you can catch electrike, mareep, registeel, zapdos, voltorb.ect. you can also find steel types there PS:Pokemon crater is closed now. But you can go on www.tppcrpg.net
You can't find Registeel in Pokemon Platnium. You just migrate it in Pokemon Ruby, Pokemon Sapphire, and Pokemon Emerald.
...You CAN'T!
cheek seribrii.net
you find it at map 5 or at that place with electric Pokemon
go on Pokemon crater
in your house
Pokemonbattlearena.net
Registeel is a Steel type pokemon.
you can rarely find larvitar.