Baikal Shotguns ...
I have a Baikal Bounty Hunter (Single Trigger) that I bought used.
I took it to my gunsmith who found that it had been 'improved' by a person whose 'improvements' were, according to my gunsmith, 'butchered'.
My gunsmith went to EAA three times, each getting a person who swore that the previous person did not understand his needs, and would send seers for the single trigger model. So my gunsmith ended up with three sets of seers (for a double trigger model) that did not work. So he is having a friend weld up some extra metal on the old seers, and will then file them down to fit.
EAA is worse than useless ... there are about seven cues one must work through in order to talk to a real person. Add to this that they no longer handle the Bounty Hunter series (it is now being imported as a Model 220 Spartan by Remington). When Remington was asked to help with a Baikal, I was given the 800 number for EAA faster than one can pass a hot potato.
The Canadian supplier for Baikal said that the translation of the gun in its manual was labored, and to send the exact number from the exploded diagram and they wourld 'try' to get the parts needed.
Don't know if the problem is the same with the coach gun, but I think your gunsmith is going the right route by just making the part himself ... it will probably be quicker, less costly and less frustrating.
It is really a shame, cause this is a REALLY nice shotgun.
BTW, my gunsmith also tried to get the parts from several aftermarket dealers, including Dixie Gun Works ....