Major problem with this achievement...NO ONE plays this game online or at all for that matter lol. Unless your really good playing guitar with your toes, your gonna need a friend. If your friend is a novice, have them play bass. It usually has half as much notes and is a lot easier. Put the song on Easy, and both of you play a song. 300 notes in a row should be no problem.
If you need someone to play with to get this, PM me, I check my message a few times a day. I can guarantee getting this for you