Just a thought, but you could 'make' your own exemplars using Adobe
Photoshop. Scan in or copy portraits into Phbotoshop, adjust the image
size, use the Threshold tool to turn images into black and white,
adjust the ratio of black to white and print. The images could then be
traced onto tracing paper which in turn could be cut and used on
templates that would be traceable not only on black paper, but other
color paper as well. Then simply cut out traced shapes on adhere to a
background sheet of paper (again, other colors than black and white
could be used, perhaps even a watercolor or ink wash background...
The students would actually be able to work the portraits using this
method and get some valuable hands on time with technology and art in
addition to the aesthetic concepts that also were being addressed.