You must have a LEGIT Shaymin. It's Original Trainer (OT) will be TRU, and the OT's ID Number will be 02089.
Once you have that Shaymin, make sure it is in your party. Go to Floaroma Town and speak to the blond close to the sign with Floroma's map on it. She will notice the Shaymin and give you Graceada Flowers.
The Gracidea Flower is only in Platinum. SORRY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
You can't get the Gracidea Flower by showing the lady in Floaroma Town a Shaymin if you have already gotten it or if the Shaymin is a hacked one or if it was caught in Pokémon Diamond and Pearl in the Flower Paradise because the Shaymin needs to have a Fateful Encounter flag on it.
the gracidea flower
you can't you can only get it on Pokemon platinum
Nintendo event
This is a rumor of how to get it.
talk to the lady near the honey man and you get a flower
Somewhere in floaroma town
route 224. {flower paridise}
You can't. It is specific to Platinum.
North of the Pokemon league (Take the seabreak path)
Flower Paradise (requires Oak's Letter)