The best place to start is Wikipedia: http://en.wikipedia.org/wiki/Stereology.

Most active research in stereology is done in medical and biological community.

In engineering, in USA, Prof. Rhines and Prof. de Hoff, both of the University of Florida at Gainesville did a lot of pioneering work. The stereological researchers active in engineering in USA are mostly limited to the "progenies" of the Florida school. These include (and I quote off-hand): Prof. Arun Gokhale of GeogiaTech and Prof. Burton Patterson of the University of Alabama at Birmingham (who was my guide at my first attempt at PhD).