Try the parts place Try thePartsPlaceinc.com they have one for the 70GS, they mave have yours as well. Good Luck Bert
Frank i dont think anyone repro's the metal screens but they do repro the plastic ones. every now and then a metal one pops up on ebay.
Couldn'T find one for my wifes 68 so I went to home depot and bought some 1/4 square mesh wire (galvanized) and used it. Depending on where you are you might be able to find small size stainless mesh wire also. The H clips that hold it in were the hard things to find. Be careful when you remove them, they snap easily
Try Ames Performance I have had some luck with those kind of parts from Ames Performance. They are a well know Full Size Pontiac and GTO supplier. Much of the 68-72 A Body GM parts are interchangeable. You can get their catalog on line. Very high quality stuff. Sagesenior