I am not aware of any freebies. The Mastercam Book by Lin and Shiu is about $80 and generally the most cost-effective learning tool.
You should also look into courses at your local tech school. But ask some tough questions before enrolling. Many tech schools, particularly here in GA, use the machine tool programs as eye candy for politicians. You may find the instructor knows less about Mastercam or even machining than you do. There are exceptions, of course, and some have excellent programs.