If you want dried, look for turtle beans. Ocado sells them, but they are write pricey, I one of my big tescos had them and they also sold them at the metro in town, but they have been out of stock for a while. I had a long discussion with a staff member about how black beans were not the same thing as black eyed beans.
I usually get mine from a caribbean shop in town (they do kraft mac and cheese, look aid, and malt I meal as well). The brand I get is Tropic Sun or something like that.