Omega Case reference 135.010 Movement clip

Hi,
I'm hoping someone might be able to help?

I have an Omega case reference, 135.010 for a Calibre 601 movement but it is missing the 'ring', or 'clip', not sure what it's called, that is rotated to hold or remove the movement. I have provided a picture below.

I have tried searching for e-clip, spring clip, spring movement holder, etc, for case reference 135.010 without success. I'm not sure if the terms I am using are incorrect or if Omega use a completely different descriptor for the item.

Any advice would be appreciated.

Thanks in advance

Regards
Seneca

Thank you @JimInOz and @Archer