There are more deities than the gods, and clerics need not be restricted to only those who reside in the Outer Planes.
All tagged elder evil
Cult Boons - Homebrew
Cults often swell up around powerful fiends, elementals, and other ne’er-do-wells. In exchange for serving the entity, they are given powerful, supernatural gifts.
Homebrew - Warring Powers
A simple system for dealing with combat between the gods.
The Planes: Far Realm
A realm far beyond our own understanding - it is the home of the Elder Evils and aberrations. It’s corruption is slowly spreading into the multiverse, hoping to transform it into an extension of itself.