you have to obtain the members card through mystery gift.(it may be possible trough AR.)
With the Japanese event or mystery gift
you get it through Nintendo event or mystery gift on Pokemon pearl platinum or diamond
You can get the member card in diamond and pearl but the event for it in platinum is august 3rd to September 13th (you have to have wi-fi connection to do this)
you have to get it via a wi-fi event, unfortunately it ended last year. however if you have a friend who has it you may be able to "get via friend" on the mystery gift menu
at a Nintendo event
you cant.
Mystery Gift or using Action Replay
you have to get the members card from mystery gift.
You need to have downloaded it from the Mystery Gift online event that already ended so now, you need to use an Action Replay with the correct code.
Not without cheating
You need to have Pokemon battle revoloution for wii and do mystery gift. What are they for?