@MacEggs is correct, just use regular sheet steel.
As the addition of anti-rust materials, whether it be galvanizing or plating, even stainless, aluminum alloy(s) ALL break down (fume) given the correct heat.
YMMV, Still more likely to get fume fever from a Small poorly ventilated soldering project than OUTDOOR grilling
YOU WILL NOT ACHIEVE METAL FUMING WHILE @ COVERED GRILLING TEMPS. (possibly aluminum)
also ALUMINUM FUMES WAY BEFORE ZINC but people (carelessly) use it in pans/food prep.
Better safe than sorry; the charcoal grate (Hotter) is NOT PLATED whereas cooking grates are...
we need to end the galvanized worry // "hearsay" debate (Fences are commonly welded, you don't see welders w/ MFF while working OUTSIDE