How do you get a members card on Pokemon Platinum?

You can't get a "members card" in Pokemon Platinum. There is no such item or feature in the game.

There are a couple of possibilities here:

* You might be thinking of the Trainer Card. This card stores your trainer's information like your name, badges earned, and your team. You can access it by talking to the man at the Pokemon Center.

* You might be thinking of a feature from a different Pokemon game. Different games in the Pokemon series have different features.

Can you clarify what you're looking for? Perhaps you could tell me:

* What does the card look like?

* What does it do?

* Where did you hear about it?

Once I have more information, I can help you figure out what you're looking for.