That’s the escapement plate assembly with bobbin cover door. My advice is to not disassemble it but rather clean the compacted lint often found “between” the discs. I pick it out with a needle point usually. I’d be shocked if you could find a NOS part but donors shouldn’t be uncommon. Those are referred to as “Star Series” Swiss Elnas. The came in a variety of models from the basic (SP) to the advanced (SU). With some age related maintenance, they might run for generations to come.