Well, if AA can't show it to you, then file a DOT complaint.
Is UA still distributing and picking up free headset?
The statement also seems to indicate they have entertainment "on all flights"

INFLIGHT ENTERTAINMENT UA RULE 0080
UA WILL PROVIDE COMPLIMENTARY AUDIO HEADSETS FOR INFLIGHT VISUAL AND/OR
AUDIO ENTERTAINMENT ON ALL FLIGHTS. AUDIO HEADSETS WILL BE FOR USE
DURING THE FLIGHT, AND MUST BE RETURNED TO UA AT THE REQUEST OF THE
FLIGHT ATTENDANT PRIOR TO DEPLANING OR AT THE FIRST STOP AFTER THE
AUDIO AND/OR VISUAL ENTERTAINMENT HAS BEEN COMPLETED.