Thanks for your replies everyone. I've found a screen printing supplier nearby who has rubylith. I'll give it a go and also maybe the imagesetter film..
In fact, I think that I still have a Ulano Co. tube lying around here somewhere with a few scraps still in it. I worked at an art supply store for a while back then and there were several similar products made by other manufacturers. Pantone made self adhesive sheets of its various colored materials and the red that was considered useful for litho purposes was a big seller. The use of computers in the graphic arts has rendered most of these cool old things virtually useless now...I wonder if anybody still sells "X-marks" in the roll-of-tape format that we used to sell out on every week. There were the self adhesive films used in layouts and non-adhesive sheets that could be cut to be used as masks for the borders of artwork going into the process camera. I don't know if this stuff is still around but they seemed to use an awful lot of it in silk-screening back then. One of my buddies was an absolute master of photo-serigraphy and I used to use my employee discount at the store to keep him in Rubylith.
How I loved the smell of screen-wash in the mornings....it smelled like art!