For the steel H-channel, you can probably clean it up and re-use it. Basically, scrape off the worst of the rust, file the surfaces relatively smooth, polish the ends of the blades that will show, and get it nickel plated.
If you really need a new one, it's probably easiest to machine a replacement from a small bar of 1018 steel. It may take some searching to find some mild steel H-channel in that small size. I've never really looked.