あなた can check on YouTube (or here) for some tutorials...They also give the notes in them. And I think it's a very easy way to learn!
But if あなた want to sheet music, you'll have to 検索 for yourself on Google または something. It's pretty easy to find. Just type the name of the song + artist and put sheet 音楽 behind it. It should give some results.
If によって modern あなた mean 愛 Story, White Horse, The Climb, This is Me and stuff I have the notes to them. Actually, I could igive あなた the website where to find them too :L