I'm fairly certain it could be special ordered in '71 but I could be wrong. I sold my tribute FM3 a while back. I'm sure someone here will know for sure. Good luck!
There are several references to FM3 being available as a special order (code 999) color in 1971. Though I don't recall ever seeing one myself, there is a guy over on "PantherPink dot com" who supposedly has a documented FM3 '71 Charger.