There's some great "dark" options for all those weapons, I especially like the Rularuu weapons for a concept like this.
War Mace/Energy Aura (color the powers dark) is a fantastic combo, there's some Endurance help in /EA.
Katana/Ninjutsu is a classic for a reason, would work well with your concept.
/Bio Armor works great with almost anything, is a top tier set for damage with great survivability, you can re-color or minimal FX most powers into a dark concept, but there's a few powers that still use the biological type effects. With some effort you could explain that as darkness stuff too though.
/Shield is great and has some good designs for a dark concept.
/Super Reflexes is great but beware it has no endurance tools, you can fix that with IOs and especially Incarnates, but you'll be out of breath a lot while leveling a, for an example, WM/SR.
Plenty of other sets but I've got the most experience with those.