There is someone on Ebay selling S type mufflers which are more like Z types. The Ebay pipes do not have bends but are cut @ 45 degree angles and welded. They were discussed in a recent thread.
I recall seeing reproduction S pipes in the past but they were threaded and used old stock threaded tecumseh mufflers on the end joined with a coupler.
I think Marcus tried his hand at this as well. As I recall, he ended up with a better result.