Sticking to fashion, some aftermarket brand sell exhaust muffler and exhaust manifold.
First, remember the heavy genuine manifold:
We can find two different types of manifold, with a different way to link cylinders.
First, the Honda way: front exhaust tubes are weld together, same for the rears ones.
Factory one, 4 in 2 in 1:
And an other release, with a complete line for the front cylinders and an other one for the rear:
The front manifold is design to free space for an oil radiator if needed.
Other example with the brand Devil:
Other solution is to link tubes in diagonal:
But perhaps the best solution is a direct 4 in 1:
Or the Martin with the muffler directly welds to the manifold:
Other brand were sell only in Japan so for 400cc bikes. The shape of the front tubes is very particular:
An other one more like the genuine one:
This one was made by the brand Over.
And if you can't find your dream, perhaps you need a 4 mufflers kit: