Theatre 2-way communications

Does anyone know where to get four reasonably good quality two-way tranceivers for backstage/lighting/sound communication? We are looking for Wireless headsets to do this job as we cannot hard wire a system. We had a set of Realistic FM Tranceivers, but they are becoming unstable (and new ones seem to be unobtainable).
Any help would be very welcome on tommyers@netspace.net.au