RWS is the only manufacturer that I definitely know of that makes 9.3x64mm brass.
Sorry I'm unable to access another site that had different types of Bertram brass on it to verify if they make it also!
RWS brass is very good to say the least, I've reloaded each a minimum of 20 times & only annealed recently after 25 years of service. Still no apparent head separations on checking after cases sized & cleaned. And no these aren't pip-squeak loads!
93x64mm