Make one. It is the only way to get what you want. I have a prototype now made of very thin aluminum and it works great. Mounts to the headers via stainless clamps and to the inner fender well with a bolt and rubber insulator - it is made to flex. My carbs are cool to the touch after sitting in traffic or a 6 hr drive.
I'll be making a nicer, thicker and anodized shield very soon.
For the part you describe. It was for a G54 Skyline (the one that came with triple Webers)
There also were some available from Nissan Comp a few years back...
Otherwise you can make one as Matt said. If you can get Stainless steel, it works as a shield a bit better, as it doesn't conduct heat as readily.