Here's some good news for Americans who own Pokemon Pearl and Diamond. According to Serebii.net (you have to scroll down a bit to find it) there's going to be a Nintendo Event distributing Darkrai (that starts with Spacial Rend and Roar of Time, moves that are supposed to belong only to Palkia and Dialga respectively) at participating Toys 'R' Us stores this Saturday and Sunday from 12 PM to 4 PM. Although this isn't officially announced on the Official Pokemon site it does mention that Darkrai will be able to obtainable soon.
So if you're interested in getting a Darkrai now's your chance!! Assuming that Serebii is right about this event...