Storm Pike

Shapur in Underground River carries Storm Pike and will drop or willingly give it to the party as a reward for Drow Runaways quest.

In-game description
"Storm giants seldom do favors for humans, but when Threk Boltwielder was saved by the wizard Alimor, Threk offered his services as a conduit for the wizard's enchanting spells. Alimor borrowed a lightning bolt from the storm giant to craft this halberd for his companion, Haldus, who had often complained about how the party never found any magic halberds despite it being his chosen weapon. Haldus was so excited by the storm giant's gift that he wielded it immediately, striking a boulder that happened to be nearby, and was promptly struck dead by the captured lightning's power."