Omega De Ville 511.286 Crystal?

Hi, I’m new to this forum and tried to find help here while restoring a watch for my fiancée.

I have a vintage manual Golden Omega De Ville dial on a cal. 485 with case 511.286 (gold plated with steel back) but I’m missing out on this faceted crystal for the case.

Does anyone know where to buy original Omega crystals or what part number I should be looking for?

Thanks for the help in advance!