User blog comment:NovaSolaris/How do you get UR if you are a free user?/@comment-24819050-20140616232209/@comment-24472911-20140617013315

This is by far the most reliable way short of going for Harmonia in AB. However, the UR reward is given to the one who ranks 1000, 2000, etc., so it's possible (but not probable) to win it from there.