Adobe Studio Exchange has a set of gradient maps including a platinum simulation
here.
Another popular method is to add a layer filled with R153 G102 B51 at 20% opacity then a Brightness/Contrast adjustment layer with +20 on Contrast.
You could also do it using the Mode/Duotone -> Quadtones option, although I don't know of any particular settings -- once you'd worked them out you could save the quadtone settings and apply them easily.
How useful all this is depends on your printing. If you are taking it seriously there is a whole field of specialist warm and cool grey inks and curves for printers that you could get into.