If you are looking for game statistics for the various creatures, they have existed since 1980 or so in various forms. There is nothing for 5e yet AFAIK, but WotC published a 3.x (sort of between 3.0 and 3.5) d20 Call of Cthulhu book years ago that statted out a bunch of Elder Gods and Great Old ones that should be easy to convert. They also published a 3.5 book called Elder Evils that had a more generic take on the same concept, and its contents should also be useful/easy to convert.