Thank you all for your replies. I have tried contacting a few different companies with limited success. However I can source replacement microphones once I know what I need. While the aux power outlet would be a nice solution I'm not sure its feasible with the fleet size.
My current microphone is a 50 ohm Electret.
I'm surmising I need to try a 5 ohm Dynamic, which I've seen in M87 and M101 flavours...
