You can buy them in supermarkets, but you need to look out for the natural, undyed (not yellow) ones - usually marketed as 'natural' breadcrumbs. If your blender's on the blink, you can dry bread in the toaster or under the grill or in a low oven, then grate it or crumble it between your fingers, or if the bread's really dry, you can stick it in a plastic bag and bash it with a rolling pin.