Obviously, we need to search the ancient Sith tombs for treasures and dark lore. Also, since most the more impressive (and therefore treasure filled) ones should date to the time before the invention of lightsabers, we might be able to find a dark side aligned sword. Now I hear you thinking "what good is that?". Well imagine the inevitable situation where we encounter a jedi and their internal dark-side-o-meter is going off like crazy. A fight ensues, they pull their lighsaber and we pull our sword. They think "Hah, this dude's not a Sith, just some force sensitive dickhead with a sword". We fight for a bit, pretend to start losing and then whip out our saber for that "Hahaha! I really am a Sith! Hahahaha!" effect.
Anyway, that's my plan. Oh, and according to the lore, such a sword should have a thingy (I wanna say "cortex weave") that means it will actually be able to parry lightsabers without melting.