I think the Earth Plate is hidden somewhere in the Tree of Origin.
You also fight Heatran, Zapdos, Moltres and Articuno there.
Oh yeah, I also think there should be a item that increases the rate of a rare Pokemon appearing.
EDIT: I tried to get the Mystery Gift. Still doesn't work, it just crashes the game.
EDIT2: Is Celebi inside the Mystery Gift? I'm wondering that because if it is, since I already have one, that might be the error.
EDIT3: I was using Coronation's link and figured out it was actually just another link to the download for Pokemon Raptor EX Version 1.9.
EDIT4: I just tried enxel's link (above) and it worked. Well thank you enxel; but now I have TWO Celebi's. The one obtained from the fight in Healing Forest, and the one I got from the Mystery Gift.
EDIT5: My game save just got deleted again. I'm only so lucky I saved a backup.
EDIT6: I like to make one post and edit it a lot, don't you think?
EDIT7: And one more thing; I think there should be a computer in the Torxia League Room.