There have been two Regigigas events for Movie 11 (Giratina and the Sky Warrior.)
This Regigigas was available in Japan from the 20th of June 2008 to the 31st of August 2008 to anyone who pre-ordered tickets for Movie 11.
This Regigigas was available in the United States and Puerto Rico from the 8th of March 2009 to the 21st of March 2009 to promote Movie 11.
Each Regigigas is holding a Custap Berry, is inside a Cherish Ball and has a fixed OT and ID Number but apart from that there is nothing else special about them. They do not have an Event Exclusive Move as a Normal Regigigas can learn Crush Grip by Levelling Up, Rock Slide by TM and Iron Head and Icy Wind by Move Tutor.
But if you really want one the only way you will be able to get one is if you trade for one through the GTS.
Hope I helped :)