Name of the song that plays in episode 6 and 21? What is the name of the song that plays in Code Geass R1 during episode 6 around 12:20 and in episode 21 around 13:02? Where can I obtain this song?
episode 6 around 12:20 


The title is School Festival!


  episode 21 around 13:02


The title is Alone, sung by Hitomi.


  Where can I obtain this song?


Well both song included in Code Geass: Lelouch of the Rebellion Original Soundtrack 2, you can purchase the copy in some online store, such as this one in Amazon. Or if you mean where you can hear it online, hard to decide the legality of the source, so I don't think it can be put here.