Has an AFL game ever ended 76-21?
Exactly once. On August 1, 1964, Richmond beat Fitzroy 76-21, and no AFL game before or since has ended that way. When it happened it was a scorigami, the first 76-21 in league history.
That makes 76-21 the 3836th most common final score out of 6,607 that have ever occurred in AFL. One point away, 77-21 has happened never and 76-22 has happened never.