Unfortunately not. There was an event for black and white but that's all for gen 5 and darkrai trading is another option
Nope. The only way to get it is via trade or migeration with the PokeTransfer. It was avaliable as a Mystery Gift in BW however, but that has passed.
Actually,it is not possible to get darkrai.There was an event for BW,if you got that darkrai,u could trade or poketransfer.