Well it must depend on the area you live in...
Well it must depend on the area you live in, because I also tried to buy some and a lot of the auto parts places didn't even know what I was talking about. I finally found some at our NAPA dealer. They had two types, medium and fine... And it was about $3 dollars a sheet...
You should find it in the plumbing area of the hardware store. Its used by some folks for cleaning copper pipe before soldering.