Ninjask can be an option, being RU in our Tiers. It can just use Substitute and gain Speed Boosts so you can Baton Pass it to your Nidoking, but you will something to get rid of SR which can destroy Ninjask.
Girafarig, Venomoth, and Masquarain are also options because Girafarig can learn Calm Mind, Agility, and Baton Pass while the others can use Quiver Dance and Baton Pass.