Unfortunately, Nidoking's natural movepool is pretty lacking even though I always loved this mon with its awesome design and shiny. That being said, you can't really get the full effect of Nidoking since running either a Phyiscal or Special Nidoking requires TMs such as Earthquake, Ice Beam, Thunderbolt, etc. The Breeding Guide / Recommendable Sets can help you try to breed a Special Nidoking but you're probably not gonna do it.
Anyways, I would recommend using a different ground type such as Diggersby or Donphan for Corey.
EDIT: According to the In-game Item Guide V2 (E15-proofed), there should be one in the Obsidia Slums.