Extremely realistic, and museum quality (lifelike) mannequins are expensive, and it would be cheaper to hire a union extra to stand-in for your lighting tests.
Inexpensive mannequins (that are just made for "holding clothes" can be bought from Supply Store Warehouse @ (800)823-8887, http://www.storesupply.com.
That being said, using a frozen, "dummy" for lighting tests is not really a good idea -- no matter how much make-up you put on it!
The breathing, moving, "dummies", with real flesh and eyes, are always the way to go.
Call your local university theatre and film department. You'll find there are students who won't mind standing in .....for the experience of learning from the process.
I used a mannequin to demonstrate lighting throughout my web site at EFPlighting.com I would have preferred to use a real person but because of time restrictions some of those demos took me several days to complete and using a human was not an option. It worked well and "Shirley" has become part of the site.
Question: What model is 'Shirley'? Is she just a torso set on a stool?
Here's my reason for using a manikin - we have a number of complicated shots with a dolly on curved track in some - between focus pulls, audio and lighting (talent and background) I need lots of footage to analyze and then perfect with live talent. We are constantly moving things around in sculpting the scenes. It's too much to ask a person not to move for lengthy periods, etc. I need a dummy!
I found the company on Ebay, it's the "HD Mannequin Supply" search under full size mannequins. Shirley is a full size mannequin but I propped only the top half on a chair. It was the cheapest one that I found and the one that looked more realistic, I believe the model number is the AU-10