Where is the white flute on Platinum?

At the Hotal Grand Lake, there is a girl who lost her Suite Key,

Go to the main entrance and use your Item Finder poketch app.

It should start blinking. Go to it and press a it will then say

"(Player) found Suite Ket!"

Then return to the girl and she will thank you for finding the key, then she runs inside

Enter her Suite and talk to her again

She will give you the White Flute

The White Flute will make wild Pokemon less likely to apear in tall grass

Note: It is NOT a Key Item, just a regular item