Small marks can be polished off with a special cloth. Unless you do unspeakably terrible things to your ball, it will not break. You can get a ball from one of the juggling stores listed in the next section. If you cannot afford to get a ball, or you need to get started right away, try an old lacrosse ball, as they are about the right size and weight. Still, it works alright for practicing.
Pool balls are too small, but better than nothing.
Actual crystal balls are too heavy, too fragile, and don't grip well enough, but can be played with for brief periods over padding. The author of another CJ site has a page about CJ balls . You may be able to teach yourself from online videos, or get someone you know to show you moves, but if those aren't enough I suggest The Book. Some juggling catalogues also carry it. Once you master a reasonable amount of the material in the book, you will be able to create new tricks and routines yourself.