Hi,
I just went through this and ended up getting a used piece from 69gtam (aka Giuseppe, of the thread "any alfa part i've got it"). It was pretty hard to find... I did start a thread a few months back that might give you some leads - various people replied saying they had one, but the deal didn't work out for one reason or another. IIRC they had the GTV6 ones at APE.
I actually had a factory cowl piece which looked somewhat like the correct piece, but turned out to be wrong (too narrow from windshield to hood, I believe). My assumption is the Alfetta GTs didn't change over the 5 years they were offered here, so it would probably be wrong for your car as well.
Good luck, and let me know if I can help some more. Unless the vent grills or some of the other more complex curvy bits are rusted out like mine were, you may be better off just patching it (since it's welded instead of a bolt-in piece).