The Product Moments is accessible through the GUI’s Analyze > Mass Properties > Area Moments.
However, it is lacking in the RhinoCommon class:
FYI, I want to access it through Grasshopper.
Also, the WorldCoordinatesProductMoments is available in RhinoCommon, but I believe the Huygens-Steiner theorem of transport only applies when the original axis goes through the centroid of the surface. If anyone has a clue on a more general transport theorem, I am also interested.