I think this is the part you are looking for:
[URL=http://parts.americandj.com/ProductDetails.aspx?ItemNumber=Z-3022000035 &ProductLine=PART&Qty=1]Starball Belt[/URL]
Even so, double check to make sure. Either visit the Parts site or call Service. In my case, I'd do both.
If it's the right part, it's only $3.00. Let's hope that's all your beloved Starball needs to get back up and functional. I also suspect that if you already know the belt has broken, you've disassembled the fixture. I always encourage users to make their own repairs, it's a good skill to have.
Let us know how your repair goes.