I'm writing a novel & need help coming up with the weapons. I've got the sword for light element, hammers for earth element, & a spear for ice element. I need help with weapons for darkness, water, fire, wind, & lightning. All help is appreciated?

Well, I really enjoyed Tyto's other suggestions...! You could use those.

For water: A trident would fit nicely here, I reckon. It can have an intricate wavy pattern etched on its pole, giving the illusion of flowing water! 

For darkness: All I can think of is some form of gun..?. This can be simple as a pistol or revolver or as grand as a submachine gun... It can emit some sort of ominous projectiles as dark and rapid as a shadow.