Borla or Burns is the only company I've seen turn out stuff like that....otherwise it probably is hand made.
Looks to be spun rather than rolled...the radiused exit of the cone is a top notch touch....usually only seen on "spun" parts.
thing is, they come with these really nicely turned, aluminum reverse cones that look a lot like your image (more than they do in the british-usa website / they're not chromed). i've since ended up using the cones on different exhausts. i don't know how to find just the cones but if i can find a straight pair rolling around, i'll let you know.
that would be great. my sl350 has a 2 into 1 set up where the headers and muffler have been welded together. i'm not concerned with what material the cone is made of because theres a fare bit of pitting on the the pipes so i'm going to black the whole setup.