In most large towns, there are sheet metal shops specializing in stainless steel. You could get one of them to cut a repair panel, drill it for pop-rivets, and then supply you with stainless rivets. Have them put a very slight "hug edge" on the panel (they'll know what this is) so the corners and edges will not stick up. You'll have to buy your own pop-rivet gun, but Amazon sells them. Do NOT get cheap Chinese rivets!!!! Once everything is in place, cover the edges and rivets with silver Gorilla tape.

Without seeing the uncovered panel and track, I'm not sure whether you'd repair the panel before or after fixing the track. But I am 90% sure some version of this will work for you.