If you've gotten this achievement on Rock Band 1, and have exported your songs or DLC, just do it on that one. If not, try it on Today by Smashing Pumpkins, that one is pretty easy, just watch out for the chords to hammer ons. Or do it on Nine in the Afternoon by Panic! at the Disco. A little more advanced, but should be manageable. It's pretty short and has a simple guitar part. DLC-wise, Charlene is probably the easiest. It's free, so no worries.
Also, another note, you can over strum for the 100% achievements, just hit all the notes. All the 100% achievements can be done in local tug of war, which is easier because you get less notes then you usually would.