There are a lot of interesting facts about the OSI parts. In fact, a lot of it were being used in other cars. Most of the mechanical parts are from the Ford Taunus 20m TS but there were several other donors. For instance, the ashtray is the same as the 1966 Maserati Ghibli. The horn button is the one from the Fiat 500 and 600. The front indicators were used in the Alfa Romeo Giulia. Below is a compilation of facts that I found. If you know something else like this, please let me know. I am pretty sure that the back indicators came from some italian beauty.
The OSI-IG sometimes promotes the reproduction of panels or rubbers, as long as they have enough people. Check their site.
As you know, Officine Stampaggi Industriali was in Turin, the Italian motor city where Fiat and Lancia are based. A lot of car related industries were, of course, nearby, like OLSA and Carello. By that time, OSI just looked for easily available stuff in the neighborhood. The good thing is this makes easier for us to find spares.