Lupe Pintos (Edinburgh, Glasgow & mail order) have them, but i just use the crushed, dried jalapenos that you get from Cool Chile Company. I normally order from their website, but i have seen their products in Sainsburys... you know how they have a display rack of gourmet stuff, like fancy olive oils, etc at the end of one of their aisles?
I just soak them in water for a bit to rehydrate them, then add them to whatever recipe.
