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I think I saw some of the fake parts sell on etsy. as the original ones are really rare, I would rather get an aftermarket one as a temporary solution until an original shows up
the watchmaker put the Bakelite bezel insert in the ultrasonic cleaner. It came out broken and transparent.

I am in the same boat. I bought an Omega Seamaster 60 Ref. 166.062 as a restoration project. Half way through and after sourcing all NOS parts, the watchmaker put the Bakelite bezel insert in the ultrasonic cleaner. It came out broken and transparent.
i have been looking 2 years for a replacement and am getting desperate. I have seen people re-manufacturing bezel inserts using moulds and acrylic but only for Rolex and funnily enough. Seiko mods. I would have zero issue having a bezel fabricated if only I could find someone to do it.
Things have moved on a bit and after Christmas I intend to post a picture or two.
On Friday, after 12 months, I finally got my completed watch back from OMEGA. They were able to repair the dial such that it didn't need a re-paint. Which was great news.
I then found a NOS Bezel for my 166.0027 which means that it now has the original face, date window, hands and a new bezel which, with the aged lume-dot matches perfectly.
And as a consequence(!), I also have a bakelite bezel that was fitted to the watch and then taken off before it was worn (in fact, before it even had a strap fitted). All of the work was done by OMEGA.
I know that it doesn't help you but what 'they' say is true, sometimes original bezels can be found.
Also, I believe that as 3d printing technology improves, aftermarket bezels will appear again at some point. And given that OMEGA have no problem supplying other parts for watches, it must be possible that they will choose do it themselves.
As for there being suppliers of good quality that are alternatives available now, I'm afraid that I tried very hard to find one and failed.
Ooooffff. I'm surprised a watchmaker put it in the ultra sonic.
A gentle clean with a damp brush I would've thought.
You're not after one of these are you? https://ewatchparts.com/bezel-insert-for-omega-seamaster-watch-36-x-31-blue-silver-part-ewp009992