Grant that is a truly beautiful machine. Thank you for the warning on the plastic parts. That is the one big flaw nearly all later model (late 1960 on) sewing machines share. Maybe some enterprising person will start making replacements. The cost of 3D printers is going down and they will soon be affordable. Then it's "just" a matter of programming in the part. Maybe use the printer to make the part then make a mold and cast them out of metal.
Does anyone know if Bergmann was a manufacturer or just a retailer? Pictures of the machine will go a long way toward getting the help you need for a shuttle. There may be a Boye shuttle that will fit too.
Rodney