You could try louvres from a DIY shop, builders merchant or plumbing and heating suppliers - sold as fixed vents or grills. They would probably not be suitable for welding but could be riveted and smoothed in with filler - depends on what exactly you are after.
Go to the local tip and pick up an old Microwave - you can cut the louvres out of the side of that. I once used the louvred side panel of an old defunct arc welder.
