You can only get it at a Nintendo event but that already passed
So your only hope is an action replay.
The Suite Key is northwest in front of the entrance to the beach of Route 213. You will need to use the Dowsing Machine Poketch App to find it.
Truly I dont think you can get it in Diamond or Pearl version sorry.
a lava cookie
The key is somewhere just past the south entrance hidden on the floor so use the itemfinder to find it.
you can't.
You give it to the girl who is locked out of her cabin. She will give you lava cookies
its to the left of the exit of the hotel. use the item finder thingy around there and ull find it. it doesnt get you anything good so dont worry if you cant find it.
in a valley where wind is
To find the suite key you use the dowsing machine app and use it near the registration booth outside and it will be a big dot.After you give to the girl she will give you a white flute and it lures Pokemon to you.Hope I helped you.
You find a cave, go into it, then find a legendary pokemon, catch that pokemon, and then leave the cave.
you find it on the ground
which key there are a ton