One of the two knobs used to position and lock the lens board to the front standard on my Toyo 45A has always been missing. This never worried me before as my first lenses were reasonably light. I've just mounted my Tele Xenar 360mm and am now more concerned. Should I be, and if so where might I get another knob from in the UK? It needn't be an exact match, as long as it does the job.