Those are... vanishingly rare. The combination of will and power necessary simply makes them impossible for most people to conjure. Partially corporeal Patronuses are less rare but they also don’t interact with Dementors in the same way. That Harry can do one at this age surprises him, if only because he hasn’t the slightest idea how that boy collected a happy enough thought to do it given his history; that he can do one at all isn’t shocking. Dumbledore could before his death. Severus Snape can in the right situation. Narcissa Malfoy could some years ago. On the other side of the war a number of people, including both Potters, could have and Marvolo had, well, killed most of those. They were powerful enemies after all.