I can make them on my Cnc plasma, the problem though, is edge quality, I could not cut a clean edge. You should draw up what you want and fine a waterjet local to cut it for ya. If you can settle for steel, I can cut them plenty easy. And they would look great. The other option you could use is to cut them from wood, and make a template for a router to follow and you can cut them yourself. Such as in the example below. (not my vid just one I found on you tube)
DIY Intake Manifold Flange - YouTube