Some of the kydex makers will custom make a holster for you but they need your gun to form the holster.
Most of the local clubs let you shoot with anything that is a carry type holster. Maybe some of the local leather holster makers could make you a copy of an approved holster. A guy in Marietta OH made a lot of the holsters that are used at Fort Harmar. What frame size is your gun? Maybe a holster for a K or L frame Smith will work.