Would Darth Vader wear a Sgian Dubh? Absolutely he would.
The Sgian Dubh is a small knife that is traditionally worn in the socks and was intended mainly for cutting up food.
This was a custom make by Stubborn Stag. They don’t say how much they charged for it, but it’s a nice bit of work.
http://www.stubbornstag.co.uk/commissions.html#.USK8GKWsiSo
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Not to dismiss the intensely awesome geekery of a Darth Vader sgean dubh, but I think he might carry a shoto… Same idea, just, yknow, the lightsaber version.
http://starwars.wikia.com/wiki/Lightsaber_shoto
I like the idea of stamping Vader’s face on their dome…