They make specific "roll" sanders that use a scrotchbrite type abrasive. Usually that finish (a #4 brush) is done to the flat sheet before the part is formed. Doing it after the fact is a bitch 'cause it's got to be straight. Try this:
http://www.finishing.com/73/13.shtml
http://www.finishing.com/4000-4199/4148.shtml
http://www.finishing.com/73/13.shtml
http://www.finishing.com/4000-4199/4148.shtml