Because Groudon's only on Ruby and blazknight might not have Ruby (or a Game Link Cable)
If you do have an Action Replay, add a new game on the AR and enter the following codes:
(m):
A2E564FE
0FB58A54
B4564EFE
23F44BF2
GROUDON:
F655438D
3AA5C717
these will make GROUDON appear in the wild.
Happy cheating!