On the mirror...one quick fix would be to deform the ball until it's snug in the socket again. A crude method would be to use a pair of vice-grips to crush/score the ball. Or maybe a drift or punch...but you'd need to find something to place on the other side of the ball to transmit the impact to the ball.
I think this would be a temporary fix as the socket will wear out as the mirror is moved/adjusted...and it'll wear out faster than before.
Maybe the best solution is to find a used one?