Everyone is saying Portland, but I lived in Venice Beach for a few years and saw both many white guys in dreadlocks and many dudes on unicycles, although not in the same person. But that's probably just because I moved away. I'm sure a white dreadlocked guy on a unicycle in Venice Beach exists.
Lived in/around KC for a few years, same observation.
But the guy on the old school, giant-front-wheel bicycle had a top hat. So it’s possible there’s an outlier.