Link to the ASTM standards and search for toys. Or look for this standard that you will find on the Play-Doh Candy Cyclone box:
ASTM D4236-94(2011) Standard Practice for Labeling Art Materials for Chronic Health Hazards
Standards: web or article database searches may lead you to some of the standards (they may be mentioned within articles).
Government Sources: Does any legislation apply that could effect your market (ADA for instance)?