I have dealt with that situation before. Had a set of parts that I bought from a police officer in another state, and used to make a mockup of the M16 works so an animator could render it in 3D.
At least around here (Occupied California Republic) there doesn't seem to be any market for previously owned M16 fire control parts or bolt carriers. If you want to see what people look like with raised eyebrows, take a bag of M16 parts to a gun show in the OCR and try to unload them. They'll treat you like a leper or some kind of freak. Some of them look like they're about to throw holy water and cower behind a crucifix. [%|]
Brand-new parts are very inexpensive and easily available to anyone who can produce a copy of a Form 4 or other proof of legitimate ownership.
The hammer and disconnector can be easily modified to semiauto-only configuration. So can the bolt carrier (though not as easily).
See [url]http://old.ar15.com/docs/AR15-M16Parts/[/url] for more information.