As I watch the video of the asteroids being discovered, all I see is prograde orbits. Their prevalence is fully understandable and justified, but the Sun gets interstellar visitors occasionally and I see no specific reason why it couldn't catch one into a retrograde orbit. They would obviously be a minority and likely not nearly as long-lasting as these in prograde orbits, but they should exist.
Did we observe any? If so, what sort of percentage of the whole are they? If not, why?