Vintage tension ring- hard to find?

I recently took my circa 1967 Seamaster DeVille to my local watchmaker to get going after several years in storage. The same day that I picked it up, the crystal popped off nowhere to be found. I noticed it when I took it off before bed. I took it right back to the watchmaker and he has had it for nearly six weeks claiming that he cannot find a tension ring that fits. I sent him links to rings that I found on eBay but he claims that they will not fit. Is it really that hard to find the parts? He claims that looks everyday and cannot find it. He has a solid reputation online and in the community, but I am not sure what to think. I attached a photo of my other watch that is identical except for the face.

He said I need the tension ring- that the crystal is easy to find. Perhaps he means bezel, but I asked him several times.

Best you post the actual watch, but if he said the crystal is easy to find. It's most likely the ring in the crystal and they come with it

You'll need to know the case reference number (inside case back) and caliber of the movement to order a crystal from a parts supplier

If a two piece case. You will need to get the information from him