One thing that might be able to be added is Cupronickel, aka white copper. It's most common modern alloys are 55/45 and 70/30 mixes of copper:nickel and it has a white color. Older mixes tended to be 75/25, slightly more brittle than the 70/30 mix, but still rather strong and weapon-worthy. While Europeans didn't rediscover it until the 18th century, the Chinese were using it as far back as 300BC and used for weapons. It was also widely used as a decorative metal with the same coloration and shine as white gold by the Romans and Greeks.
As for material properties, it is superior to Bronze and Iron, though not as strong as the steel we see in game.
Also if we're going for the Greek version, it was called Orichalcum alongside the arsenical bronze version - both had the same name, with the cupronickel being somewhat stronger.
Personally I think it would be a nice thing to see.
Chinese mix: Used a copper bath with small chunks of nickel ore paktong (nickel-arsenic-cobalt ore. Also useful for cobalt) added in a smelter. A small amount of tin was then added, and the slag was cleared.
Of a note, I'd also like to see cobalt added as a metal, as pure cobalt is very similar to iron in material properties, and would be a nice thing for volcanic embarks. we could also then add a couple more ores which would be cobalt-nickel or cobalt-copper containing (multiple metals). It is able to be processed in copper-arsenic ores and copper-sulfide ores, as well as simply sulfide based ores like cobaltite, through removal of slag and re-smelting. (cobalt is the slag in these reactions - you just keep smelting the slag till you get just cobalt)
So while not used in antiquity, I don't see a problem with dwarves making cobalt bars. Seeing as all they have to do is smelt it multiple times to get the metal. (unless of course, I'm mistaken by what I've read online, though I do know -most- processes to acquire cobalt require electricity, and all the processes which involve nickel-rich ores)