If you're not too hung up about originality, a lot of auto parts stores have heat riser tubing. This is flex tubing that connects the exhaust manifold heat shield to the the snorkel on the air cheaner housing. You need to know the diameter your car needs. Save the clamps off your old ones so you can attach them to the heater box and registers. You might also be able to install this stuff as a sleeve in the duct work you have now.
Typically it is made of metallic foil. Give it blast of flat or semi-gloss black paint before you install so it isn't an attention getter.