You will need three things:
1 - an amplifier with a VERY high input impedance (around 100M or 1 G ohm input impedance). Finding a MOSFET is an easy thing, finding a 100M or 1G ohm resistor is more difficult.
2 - A 60V (or so) low noise DC power supply with a 100M or 1G ohm output impedance. You can either use a lab supply with a 100M /1G ohm resistor or build a DC-DC converter to provide the requested voltage (witha ample outpur RC lowpass filtering) and
3 - A high quality (very low leakage) DC blocking capacitor. A small value (1nF) will do the job.
You bias your electret mike cell with your DC supply using the series resistor and
you use the capacitor at the electret cell output to prevent the DC voltage to reach the Hi-Z preamplifier.