Weston UK, can and will make whatever header you need. They just need the exhaust dimensions or the engine manufacturer and the dimensions of the header. The 'S' header for the Magic or Skymaster is actually pretty simple. The offset header for the Aurora or Citation should also be easy to make. Kevin Gribben, mentioned above, made some very nice adapters for OS and YS rear exhaust 61s which you could use Rossi headers on. You might try sending an email to Leo at Ballistic Aircraft, Co. He might have some adapters and he was selling Rossi products.
Definitely a shame about Mac's Products and Hatori, too, but I guess the just wasn't enough demand.