In an attempt to prevent law-enforcement personnel from infiltrating their organization, the Mexican Cartel 'La Familia Michoacana' required prospective members to commit a murder and eat the heart and/or other organs of the victim;

http://www.dailymail.co.uk/news/art...-says-drug-gang-members-ate-human-hearts.html

La Familia Michoacana had thousands of members from it's founding in the 1980's until it was disbanded in 2011, meaning that there are thousands of actual cannibals living in Mexico who could have been recruited to serve as the walkers in the episodes, like this one, that are being filmed in Mexico...