http://www.gweep.net/~rocko/PZM/
http://home5.swipnet.se/~w-50719/hifi/qsxm2/
This wireless microphone transmitter is claimed to have coverage range up to two kilometers
http://w1.859.telia.com/~u85920178/tx/bug2.htm
replacing amplifier tube with FET
http://www.ethanwiner.com/U47-FET.html
http://www.paia.com/phantom.htm
simple device for detecting audio-frequency electromagnetic signals, such as those emanating from a loudspeaker, or it's cable
http://free.prohosting.com/~pointsrc/audio/induct.html
a collection of phono preamps and equalisation circuits, one of which is sure to meet your requirements
http://sound.westhost.com/project25.htm
an electret MIC is the best value for money omnidirectional microphone you can buy for 90% of microphone application
http://www.eclectic-web.co.uk/index.php?jump=mike/electret_a.htm