Oak's Letter is obtainable through going to one of the events. You can also get it through hacks.
YOu CAN GET A SHAYMIN BY getting the preffesors oaks letter from an Pokemon event or by using an action replay. for more info go to yourpokemongo.webs.com
oaks letter
u need oaks letter that's where shaymin is get oaks letter.
that was an event to get shaymin! i dont think you can get it the only way to get oaks letter is from an AR code
go to where Oaks letter is and go to where Shaymin is then that is where is should be
first you have to get oaks letter on mystery gift if you get that then i don't know
You can trade with someone who has Shaymin, but that's your only option. To get Shaymin, you need Oak's Letter or Action Replay.
you cant its a key item but you gan trade the shaymin
you must have oaks letter. that event hasn't even happened yet. or use walk through walls to get to flower paradise.
You will have to wait until a Nintendo event is out which can give you the oaks letter, and you have to catch shaymin before you get the flower. Heres a list of all events: http://bulbanews.bulbagarden.net/wiki/Front_page/Events
No. The Shaymin event (oaks letter) in Pokemon platinum is not shareable. ~Bellafuzz
Other person's answer: get oaks letter and go to the tablet oak will be there and shaymin will appear My answer ;In order to get the lengendary grass pokemon: Shaymin, you must first receive Oak's letter or invitation to tell you to go to the lab from Twinleaf Town. After, Shaymin will appear.