Preparing to go out on The-Big-Red-One I noticed that the distributor cap was loose. It seems one of the little screws that holds a clip for the cap had successfully made a bid for freedom! There was no sign of them in the garage or on the driveway so an M4 screw, lock nut and cable tie were used as a temporary measure.
I checked all the usual sources in Europe and, while I can get the clip from any number of places (including classic Fiat 500/126 part specialists), I can’t get the special screw as well. I turned to Harpers in the US who have them listed as being in stock and ordered two of each so I’ll have spares.