King Arthur makes this pneumatic sanding ball that I have heard good things about but have never tried.  They have a whole system but is a little spendy for my cheap side. 

They also have what they call their scuff and buff balls seen here.   




The last option and the one that I have actually tried is a one that David Reed Smith talks about in this article with instructions are making your own.  Make sure that you download the pattern for cutting your own sanding disks.  Lots of other good articles on his website too.  

As for disks, I found some sanding disks on Peach Tree USA (about half way down the page) that I use a lot.  

--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.