[Help] falling movieclip

I’m trying to make a small game where u are able to shot on “things” falling from the sky…
I’m done with the movement on my cannon and the shouting part but now i really need some help from someone…

what is the best way to do the following:

I have, let say, a ball as a movieclip and i want this ball to dublicate and randomly, on x basis, fall down, but i only want the screen to have a total of 10 balls falling at the same time and all of the balls has to have a unique number.

I would be very pleased if someone could explain this to me.