Here in the Nottingham area we are unduly blessed with speedo and tacho specialists as apart from the two already mentioned we also have Gaggs (see adverts in Old Bike Mart, etc.). They are in Arnold these days, having sold their previous British bike parts business a couple of years ago to concentrate on speedo repairs. Then there is another chap whose name I have forgotten who is the landlord of the Woodlark pub in Lambley village, and Paul Beck of Wollaton. So that is five that I am aware of !
Brian