Hi.
Perhaps someone knows which automobile brand/model/year is factory fitted with a stainless steel muffler ? Mercedes ? Volvo ?...
Am after a 6" round one from a wreckyard, like :

 

Mercedes certainly uses them. I suspect others do too. There are aftermarket versions (https://www.summitracing.com/parts/...MI7avYucXc6QIVRL7ACh1frwbtEAQYASABEgJUZ_D_BwE).

Just buy one. Why do you think you need one?

Since this is an electronics forum, your question is much like asking, "Who makes silicon transistors?" What size do you need?

Moreover, if you have a decent recycler to go to, it can probably help or let you browse the yards. I have done that many times when looking for a part to fit, rather than a specific part/model number.

 

Doubt your going to find a round one, most OEM car mufflers are oval. And most stainless ones are welded on. Did you look at Ebay? Just the first one that came up, didn't know your pipe sizes - https://www.ebay.com/itm/2-5-Stainl...926535?hash=item33f0e5d647:g:bAYAAOSwmUFb8~RD

 

Mercedes ? Volvo ?...
Am after a 6" round one from a wreckyard, like :

Old Toyota. But not sure what will be round.