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I assume this is for Part 15 use.
This would be an interesting project. Looking at the specs for the monitor shows it requires 5 to 10 Vrms into a 1000 ohm load. This is 25 to 100 mW so an amplifier would be needed for Part 15 use.
AM amplifiers can get complicated due to the need for linearity and probably tuning. Maybe you could investigate using an untuned linear operational amplifier circuit instead. Possibly the signal at the antenna output of the transmitter could be amplified to give the correct input to the monitor.
The signal at the antenna output for a typical Part 15 AM transmitter will be around 20 to 100 volts rms typically (after the loading coil). This is plenty of voltage but the impedance is very high and any loading will disrupt the output signal so a high input impedance amplifier would be needed. The signal before the loading coil will be around .5 to 2 Vrms so some voltage amplification will be needed but the impedance at this point is low and easier to tap without disruption than at the output of the coil.
Without knowing more details this information is just to help you plan an approach.