Well lesson learnt, don't just check the site for the part but also ask to see if they have one. I contacted Mike of Mike's Classics in Queensland over the weekend to check on whether they had or were going to get any more Superflash rear number plates and Mike replied he had a NOS one so its on its way.
He also had a set of the rear head steady's that the Superflash used, part numbers 67-974 and 67-975, so they are also coming. These were used on the American models only according to the parts supplement for the SF but I have only seen pictures of one bike with them fitted which I believe is owned by Terry Parker. Maybe they just got in the way of the carb?