The big problem with this literature, is that the incidence appears to be dependent on population. Current hypothesis is diet may contribute. To make matters worse, the subject seems to be predominantly studied in non-US hospitals.
In world populations, choroid plexus is common with reports going from 15-69% . Habenula calcifications range from 15%-32% .
There's an Iranian based study with distributions by age. I think this is it:
Daghighi, M. H., Rezaei, V., Zarrintan, S., & Pourfathi, H. (2007). Intracranial physiological calcifications in adults on computed tomography in Tabriz, Iran. Folia Morphol (Warsz), 66(2), 115-119.