I knew that there WAS a company out there making these holsters.
I know that a small portion of our member base (for whatever personal reasons) NOT to be debated in this thread - desire to carry empty chamber.
Though I disagree with empty chamber carry, it's not my place to bite your head off for doing it.
This is probably the best holster out there that will allow you to chamber a round prior to drawing your firearm and it will allow you repeatedly rack the slide while the firearm is holstered until the magazine is empty.
The only problem that I see with it is that it appears not to hold the firearm in super close to the body so you may need to somehow adapt it for better concealment. Anyway...here you go. Their website & a VID.
SLVE Specialty Equipment Manufacturing Inc. | Safety Holsters for Glock, Beretta, Browning HiPower, Smith and Wesson, SIG Sauer, Colt, Springfield XD