I don't know much about the MS3 market, but if the couple of main players (StreetUnit, Cobb, etc) don't have one, it's probably not being made. A one-off piece probably wouldn't be terribly expensive to make as it would just be some cut, bent, and welded thin gauge steel. Otherwise, header wrap and a turbo blanket are going to be way more effective at keeping heat in, though not as purty.