You cannot catch him in that game, but you can transfer him from a Gameboy game with another DS.
no you can not
Registeel is not catch able in Pokemon LeafGreen. In order to get a Registeel you will need to trade for one from Pokemon Ruby or Sapphire.
You can not capture him in pokemon black
no you can, you most catch it in Pokemon emerald
You do not need a Wailord to catch a Registeel in Pokemon Emerald. You may need a Wailord or any other water-type Pokemon to surf to the place where you catch Registeel, but other than that, you don't need a Wailord.
Only ruby, sapphire and emerald can catch registeel trade one from those games to leafgreen.
You can not catch Registeel in these games. You have to catch him and the other regis on Pokemon Emerald, Ruby, or Sapphire and migrate them to Pal park your wrong go to route 228. there you will find it.
beat elite 4
Nowhere.
In order to catch Registeel in Pokemon diamond, you need to have gotten a level 100 Regigias from a mystery event. This mystery event has passed, so you can no longer get Registeel in Pokemon diamond, unless a friend trades you the mystery event Registeel. The only other way to get Registeel is to trade him from Pokemon emerald, ruby, or sapphire.
you must catch regice,regirock, and registeel
in chroma ruin