I have no experience with the system and don't know its price point, but have you heard of the Polycon SAR system?
http://www.lifesavingsystems.com/bas...polycon1_1.htm and
AnCom | Broaden Your Communication .
It seems to be mentioned here:
http://www.pprune.org/military-aircr...nsceivers.html
http://www.pprune.org/rotorheads/346...ml#post4459112
But, why not just adapt the FM transciever leads to your helmet wiring?