Only brands I can think of off the top of my head offering anything for the 2.4L Xterra/Frontier would be Megan or Pacesetter, neither of which I would invest the time or money into swapping out for.
If I was to give you any good advice, I'd see about pulling the Manifold off a JY truck. And either take it to someone at a fab shop for custom exhausts or contact me and I can put you in touch with a man in Florida whom does everything from custom manifolds and turbo builds on some exotic cars to track cars and understands all aspects of exhaust scavenging and making it work. He's on my personal linkedIn page as a business contact.