What's the name of the song from..
 

Kamen Rider Kiva.. the song that Otoya plays on the violin ever-so-consistently throughout the series?

..And would anyone happen to know where I can find the sheet music for it?

As far as I can tell, it doesn't have a name. However, I would believe that if you were willing to do some research, you would find the sheet music under the composer "Chopin."