Up for sale is this NOS Genuine Toyota RH Radiator Grill mounting bracket
That references out to fitting the 1979 thru 1981 Celicas (Not Supra)

It might fit the 1978 but I am not sure, it would be your risk to purchase!
part number is 53223-14090, and this has been discontinued,
the orange-ish color is NOT rust, I think its a coating of some kind?!?!

So get it new, here, and not some used damaged or
rusty part you will have to repair or sandblast and paint!!