I can make some, if you can find me some fiberglass. I'll need to filter out the unsaturated polyester resins. I can do the same thing with industrial molding or even toner from laser printers if this old place has any lying around. Oh! I'll also need some calcium carbonate if anyone has some to spare. Basically, some chalk or limestone. Marble could do the trick too.
From there it's just a matter of some molds, some science, and some paint to color the balls!