You may still find imperial grub screws at the more 'old-fashioned' ironmongers (ie: not B&Q) or more established machine equipment suppliers (ie: not Machine Mart). I have a few in stock in my workshop, and I bet if you know anyone in the toolmaking trade they'll be able to help you. But it will probably be easier to cut a bit off a set screw or bolt, and saw a slot with a junior or standard hacksaw. Beware that it will be 'softer' than the proper thing though. BAH