Here's a few pictures of a 2 into 1 system I built for a CB175 that I owned. It's not quite finished in these photos but you can get the idea. I used mandrel bent sections with matching diameter and wall thickness tubing, all cut and fitted, then TIG welded together. Lots of hours and patience, but I think it turned out well. I built the muffler for it as well, but anything aftermarket that catches your fancy could be used, just a matter of matching ID and OD of tubing so things slip together where needed.
Obviously, you'd have to do everything X 2.