It's actually stainless steel (or it should be) which is a very hard metal and therefore harder to polish.
Head down to your local hardware store and they should stock polishing kits that fit up to power drills.
Get a little practice in on a bent or busted piece first.
I have found a loose mop is good for cutting then follow up with a stitched mop for the final polish.
I use a kit that fits up to my bench grinder, but if you aren't careful it can launch the metal at the floor at a fair rate of knots! Not good, especially for aluminium pieces