Subcultures, Communities, and Physical Places Where Chastity Belt Use Might Flourish
1) On a college campus
Here, I am referring primarily to the case of students belting other students, not so much to those with belts imposed by parents. There is definitely something special about a college campus: Your keyholder would always be within walking distance. I would be especially interested to hear of reports of chastity belt use among fraternities at elite campuses in the USA or elsewhere. "Getting belted" might be something akin to "getting pinned."
And, now that we have cheap, reasonably high-quality cage devices for the male, it would not surprise me at all to hear of college girls competing with one another to see who can keep the greatest number of cocks under lock and key.
2) Among the Amish
Most Amish men seem to treat their women as livestock. For an Amish man, putting a leather belt on your wife or daughter and then locking it would not be much different from putting a bridle on your horse and then locking it.
3) Opus Dei
4) Society of Saint Pius X
5) Fundamentalist LDS community
Let me begin by saying that these folks (FLDS) have a lot of practices that I definitely do not approve of: Polygamy, child brides, forced intergenerational marriages to close family members, etc. To hear reports of chastity belt use in this community would really bring me no joy.
6) Saudi Arabia
Over the years, we've heard fairly credible reports that Hal Higginbotham of Tollyboy had shipped belts to customers in Saudi Arabia, but as with the FLDS, it brings me no joy to hear about it.
7) In a Taken-In-Hand/"Domestic Discipline" marriage or relationship
There used to be a taken-in-hand.com website, but I guess there no longer is. The website had a discussion forum which contained two or three mentions of short-term chastity belt use.
8) In a "Zero-Privacy Marriage"