Unfortunately you can only get it through a Nintendo event or a cheating device - there is no other way however there's this specific Secret Key event currently going on until May 12, 2009 which is no longer available and you need to do the following in order to get it:
Wi-Fi events are region-locked so only those players with the respective region's game can access the events if they're currently online. The US and Japan are no longer holding events as of right now for the Secret Key but Europe, Australia and New Zealand will be holding them soon and here are the details. For Europe, they'll be holding it via Wi-Fi from June 8, 2009 until July 19, 2009 and for Australia and New Zealand, their events are ones you have to go to since they're via wireless and here are the locations. First for people in Australia. For people who are in or near Queensland, it'll be available in Carindale June 27th and 28th and it'll be available at the Pacific Fair July 4th and July 5th. For people in or near Victoria, it'll be available in Soutland July 9th and 10th and at the Fountain Gate July 11th and July 12th. For people near or in New South Wales it'll be available in Chatswood July 18th and July 19th and at Parramanta July 25th and 26th. For people in or near Western Australia it'll be in Carousel July 4th and 6th. For people in or near South Australia it'll be in Marion on July 18th and 19th and for people in New Zealand it'll be available in Sylvia Park on August 8th and 9th.
its a secret place
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secret key is the only 1 i know at the moment look on the Pokemon.com website to see how to get the secret key by beating either Jupiter or via wireless internet(wifi)
hes not in platinum:( try ruby
ActionReplay
You can only get the secret key in Pokemon Platinum
you need wifi do get it!
well you need the secret key for team galactics HQ
Already happening............
You can't get the Secret Key in Pokemon Platinum without Action Replay, unfortunately. You can get Action Replay from most major websites.
No, you can't mix records in Pokémon Platinum in order to get the Secret Key from a friend.
stop being a Pokemon playin douche
The Old Cheatu.
obtian the mystory event
No you have to get it again.
give him a secret key the different secret key the different rotom
check serebii.net for info on upcoming events for Pokemon Diamond,Pearl,Platinum.