Barb, that type of metal panel is called R panel. There are a few manufacturers and although the exact profile will be close, they may not be an exact match. But, it will be very close. They are 3 feet wide and if you want to close the opening completely, buy a full panel and it will blend in, except for the color. All of our buildings have the same R panel exteriors and roofs and I have helped in building some of them.
I am adding an extension to one this (or next) week. The roof extension will slide in under the existing one. Because of different manufacturers, it might not be a perfect match. Part of the roof is going to cover the slab. Close-up of the rib pattern although mine only has two minor ribs between. At the bottom left, you see a screw that locks two panels together lapping over at the ribs. That requires a screw called (of course) a lap screw. The remainder screws are a type that screws metal to wood. You may be able to use the same screws or buy them in small quantity at a small hardware store like ACE.
Take your pictures to a metal building contractor and he can advise you or help you out sourcing material.
"Duck and Bob would be out doin some farming with funny hats on." chrisstef
