Can anyone tell me where to find the piano sheet music for the song 'Sakura Sakura' by Rin?

You can buy it from sheetmusicplus.

http://sheetmusicplus.com/

Alternatively, here are a few websites for your reference. Might not be the specific sheets you are looking for but you might find something you like.

http://ffpianomelody.com/

http://popsheets4u.blogspot.com/

http://thechopincollection.blogspot.com/

http://yiruma4ever.blogspot.com/

Rin' made a their own arrangement of the traditional song "Sakura Sakura," so unless they released sheet music themselves, it probably doesn't exist since they aren't that well known. What you will find is a lot of sheet music for other versions of it.

They can be. Music is and has often been linked to emotional matters and many of the great writers of history have spoken of it as such. I also find that music is often good at arousing feelings in the listener, even when one cannot personally identify with the words of a song or the thematic content. For example I can think of the song "Forever Autumn" (which is included in the "War of the Worlds" musical) and appreciate the feelings of sadness and longing just from the tune, even though I've never lost a lover (or had one to lose). I frankly don't have a song at the moment, though I have a tune in my head...

free music is illegal

that violates the copyright laws