When I removed the injectors last time, I measured the OE gaskets and ordered accordingly. I found those on Aliexpress: Initially I measure on those thicker ones ID 8mm and CS 3.5mm. I ordered them already (material FKM) and then I spotted they someone is offering similar seal for exactly that purpose "fuel injector repair seals ID 7.8mm and CS 3.9mm - so I ordered 100 of those (AU$25). And the smaller seals I measured as OD 12mm and CS 2mm, and I ordered them in FKM (10 pcs for less then AU$4).