Opinion Needed: 2004 loose rearview mirror
#4
I will make the assumption you did try to tighten the holding screw and that it is the ball that is actually loose?
If it is the ball I would go to a scrap yard and pick up a mirror.
One thing I would try though is take some silicone and dab it into the ball socket, move your mirror around a bit then set your mirror and allow the silicone to set up. That might buy you the time to get another.
Kind of cheezy I know but who knows as the mirror is going to be tossed anyways right?