Original Budd releases with speckled silver paint, Polly Scale Stainless Steel.
New reflective finish on sets (Super Chief, Cal Zephyr) Alclad II Chrome (must airbrush) with top coat of Testor's Metallizer sealer.
Or if you are just touching up a reflective set, mix some black into the Polly Scale Stainless steel to darken it a tad and it will blend in well on small sections.