I think you'll have a hard task to find black sheep with white faces. I know of one breed, The Finnsheep, which sometimes has black wool and a white face but they are natives of Finland, The Balwen Welsh Mountain sheep has a black body, mainly white head and a white tail. The only breed in the UK that is completely black is the Black Welsh Mountain. There are fewer black sheep than white because there is less demand for black wool as it can't be dyed. That's the extent of my sheep knowledge so I hope that others can add to this.