I would try Home Depot. I got some at McGuckin's last time I needed it.
By the way, buffing metal is _dangerous_. I would also buy a face shield if you don't have one, heavy gloves, and it would be nice to have a leather apron. The last thing you want are metal shavings in your eyes or body.
If you are buffing on a bench grinder, pay attention! That piece of metal in your hands can be taken out of your hands and then it can be whipped around the wheel and back INTO and THROUGH your hand or body.
If your are buffing with an orbital sander, be sure that the metal is clamped down well. As long as it's clamped this way is not nearly as dangerous as using a bench grinder.
Good luck!