You cannot find Deoxys in Pokemon HeartGold. Deoxys has to be traded from another game to get into HeartGold. The rocks to the east of Pewter City are used to change Deoxys' forms, but you have to transfer one using Pal Park, first.
trade on pal park
You cannot find Celebi in Heartgold or Soulsilver, with the exception of obtaining one in the forest of Pal Park.
no only from pal park or trade
You have to migrate a Pokemon to Pal Park.
poke pal it from a ruby Sapphire or emerald
You can't find Groudon in Heartgold. To get him, you'll need to trade from another game or use the Pal Park in Fuschia.
you can only get celebi in an event or pal park.
By Nintendo even or Pal Park
in the lower floor of elite four building
In order to find your Wi-Fi Friend Code in Pokémon HeartGold, you first need to get the Pal Pad by going down into the basement of any Pokémon Center. After retrieving the Pal Pad, talk to the lady in the middle and she'll connect you to the Wi-Fi server which will register you a Friend Code and once it's completed then it'll boot you off. Check your Pal Pad and select "your Friend Code" and you'll see the Friend Code number that is your Friend Code.
It isint in Johto,its in Kanto in Celadon city.