Smashing video on the right hand column (or video page) about modeling faces and there is another one on push molds for faces.
The techniques in these two videos vary. One using face push molds and the other building up & modelling.
If you are familiar with making molds, you should have the
art hobby pdf on mold making, you can actually make your own molds,
instead of using plaster, of course, you can use >>>>
flexible mold making materials like this.
You can model your
'master model' piece from paper clay or normal clay and pour over the melted flexible mold making material. Once dry, just separate the clay model from the new mold, leave to dry properly before using.
For serious cold porcelain crafters, it may save you a little time in the long run. The added benefit if you are in business or know other crafters who could benefit from molds you could:-
set up a mold making workshops
sell your own molds locally or online
Have fun
Diane