I need an inline volume control knob for several microphones.
You will have to build these yourself. Stand alone in-line volume controls for mic level signals are no longer manufactured.
1) XLR type low Z volume control jack that I can plug into an XLR microphone between the mic and the mic cable and
2) the old screw-on type Switchcraft type microphone connector (for old bullet mics like the Astatic JT-30 and Shure 520 green bullet) i.e. a screw on type volume control for hi Z mics to put between the mic and the mic cable so yo control the volume (this is for harmonica playing).
1) There is very little demand for such a device;
2) It is difficult to find potentiometers that will not induce noise into the mic signal.
The current Shure 520DX has an internal volume control. Copy this circuit to build a control for high impedance mics. The value of the pot should be 100,000 ohms.
The same type of circuit can be used for a low impedance control. The value of the pot should be 2,000 ohms.