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First of all, I don't believe there is a cheat code available for the Wii that will give you all the crystals!
The power crystal you can get by completing certain levels. By the time you beat the game you should have them all.
The color crystals are a game of hide and seek.
2 of the green crystals I have found. 1 can be found easily on the first level, the second is at the Jedi Temple the second time going there. When you first enter the great hall it will be on the right hand side behind a pillar.
On Felucia: After defeating the 2 rancors, a red crystal can be found under a large rock, a purple crystal can be found in a tree by destroying it with saber or force. (Both locations are around the maps edge.)
I have the other purple crystals but do not remember where I found them.
Other than that you will just have to search for them.