The Porsche factory first made these available in 'bare' metal, not primered https://pbase.com/9146gt/image/23118818. This photo shows my same steel fenders after an 'acid dip' https://pbase.com/9146gt/image/23118819 to remove the surface rust. I purchased my GT OEM steel fender flares in 1980 from Allan Johnson, a Porsche dealer in San Diego. The fenders were delivered by UPS in a cardboard box, the flares were coated in a light film of oil.
The steel flares were later offered painted in primer to provide a bit better protection https://pbase.com/9146gt/image/153083810