Koppitz' 1968 book "Psychological Evaluation of Children's Human Figure Drawings" is still useful and includes research data. The much more recent "Draw a Person Screening Procedure for Emotional Disturbance, authored by Naglieri et al. and published by Pearson, contains useful data in its Manual. Beyond those major sources, there has been a trickle of published research. If you try PsycINFO you'll be able to identify the studies pretty easily. But there's a lot less on this subject than one might expect.