I see you're new. Try to avoid double posting, and use the Edit button to edit your first post.
To get Darkrai by an Event, you'll need to wait for one first. Wait for one to come to wherever you live and then go to it and you'll get a Member Card downloaded onto your game and you can use it to get Darkrai.
I don't go to events. Too much bother. Plus I don't use AR because I despise it, and I can't use Wi-Fi. No Darkrai, Shaymin or Arceus for me...