How do I get the secret key to change Rotom's form in Pokemon Platinum version?

I got the option to get a mystery gift and I searched for one on Nintendo WFC, but I got Oak's letter instead, which unlocks Shaymin. Does this mean that I can't get the secret Key? I have tried searching for a gift again, and getting rid of the wonder card, but it just says that I can't get another Oak's Letter. If I can't get it now because of the Oak's letter, then would I be able to get it if I restart the game? I have pearl version so I could just trade everything over to that.How do I get the secret key to change Rotom's form in Pokemon Platinum version?
Oak's Letter is the only event available on Wi-Fi right now. The Secret Key events have passed so yes it does mean that you can't get the Secret Key but it has nothing to do with you or your game. The Wi-Fi events are all up to Nintendo and they can only put 1 event online at a time for each gaming region so restarting Platinum wouldn't make much of a difference since the Secret Key isn't available anymore unless Nintendo decides to put it back on Wi-Fi again.How do I get the secret key to change Rotom's form in Pokemon Platinum version?
Its only available in Canada at this time