At US Gamestops
From January 3rd 2011 to January 9th 2011 Shiny Raikou
From January 17th 2011 to January 23rd 2011 Shiny Entei
From January 31st 2011 to February 6th 2011 Shiny Suicune
Transfer these to Black and White to awaken Zoroark in the Illusion Forest.
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At US Toy's R Us
Ash's Pikachu
From January 30th 2011 to February 5th 2011
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Celebi
February 27th 2011 to March 7th 2011 at US Gamestops
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Europe Wi-fi
Starting February 7th 2011 the shiny legendary beasts will be given out over wi-fi.
http://serebii.net/index2.shtml