Omega Cosmic 2000 Ref. 166135 / Parts needed

Hello dear forum,

I am looking for help. I have been given my father's watch as a present and it is currently at the watchmaker's for restoration.
An Omega Cosmic 2000 Ref. 166135.

Unfortunately, the watchmaker is not able to get these two parts:

• Sealing ring for the crystal (L-seal)
• Sealing ring for case back (L-seal)

Does anyone have any idea where to get these parts?
I would appreciate any advice.

Cheers!