Does this device exist? Call it External switch Box- (ESB) it would plug into an AC outlet. AC powered device A (a TV controlled by remote plugs into the ESB. Also plugged into ESB is a stereo (no remote). This is device B. The ESB would allow when device A is switched on and off so is the power to device b.
If you want to use an existing remote control paired with device B to turn power on or off for both device A and device B, I don't think I have seen anything quite like that commercially available.
However, it would not be unreasonable for a skilled hobbyist to build their own auxiliary receiver to control a duplex convenience outlet using the remote control for device B. This would be used in conjunction with the remote control used to remotely control device B.
Complexity would depend on whether the existing remote control is an infrared type or a radio-frequency Bluetooth type. Infrared is fairly simple because all you would need is an infrared receiver and a small microcontroller to interpret the serially-coded infrared signals from the remote. Determine which code turns device B on or off and use that same code to control the duplex outlet, from which both device A and device B are powered. Your DIY device would of course be powered from the un-switched power connected to the duplex outlet, so when both device A and device B are un-powered the outlet can be made "live" again.
