This is the very first time I have ever heard of a group called the three percenters.
In reference to the 3% of the population, in the colonies, that participated in the American Revolution. And now a “group”, although I think it’s more like a window/bumper sticker or t-shirt.
I don’t think there is an actual entity, like the Oath Keepers are, which is an organization of active and retired LEOs and veterans.