I have a number of Hoya filters. They are square and slot into a carrier which in turn clicks on to an adapter (step down) ring. This ring is a 55mm thread for my old film SLR. My digital camera takes 58mm. The equivalent rings for Cokin filters don't fit the filter carrier and Hoya no longer trade. Does anyone know where I might be able to get hold of a second hand Hoya 58mm adapter?