sadly you can not get Groudon in Pokemon Diamond, but there is an Action Replay code for it:
94000130 fffb0000
d5000000 0000017f
b21c4d28 00000000
b0000004 00000000
c0000000 0000000b
d7000000 00024620
dc000000 00000006
d2000000 00000000
you get groudon from a certain fossil
you cant
In Diamond version you can only get groudon though palpark or by trading with other players. It does not appear naturally in the wild.
groudon is in pal park in the mountain area
There is no real way to get groudon, but you can just migrate it, or have a friend trade it to you.
You can only get groudon if you migrated it through the pal park from Ruby or Emerald.
On the national pokedex Groudon is number 383.You can not find Groudon on the Sinnoh pokedex.
There are two ways of getting Groudon on Pokemon Diamond. The First way is trade it with people in the GTS (Global Trade Station). Or you can migrate it from Pokemon Emerald, Ruby, or Sapphire.
Groudon does not appear naturally within the game. Transfer it from Diamond pearl platinum soulsilver or heartgold.
you cant get it without migrating.
sorry you can't unless you cheat
the only way to get groudon is to either import it from Pokemon sapphire/ ruby/ or emerald, OR, trade it from pearl/diamond/or platinum.