In reply to whimbrel:
> I know it is theoretically possible to make a DIY set from plastic bottles but that option doesn't appeal as not really willing to bodge together something safety critical.
DIY ones work just as well as own brand ones, and having some is a lot better than having none. So if you can't buy any, it is really easy to make your own. The ones below are made from a big milk jug, a bit of gorilla tape around the edges little cable ties although I've replaced them with twists of green plastic-covered garden wire which is much harder wearing.