UPDATE: With the new Online Quickplay feature, it is now far easier to find other 2 or 3 people and play a long song together so that everyone gets the achievement. Confirmed working online, as it is how I got this. The original solution is below.
To my knowledge, there is no song in the game that allows you to earn that many points Solo (One instrument. Playing guitar/bass and vocals at the same time might earn you the achievement in some songs). This means you'll have to find at least another friend or two (full band would be even better) in order to obtain this achievement.
Long songs give you more Score potential: if you don't have DLC, try playing Metropolis by Dream Theater. Also remember that you can get more points by playing in Expert difficulty.
Finally, remember to activate Overdrive together, so that you get a major multiplier boost, which equals more points.