As Crossroad posts in another subject.
this module can usefull for you.http://www.ohglrf.com/upload/2010330191534162_0.pdf
But there are only 8 differents frequency.
but in thsi pdf we can read :
Carrier frequency: 433MHz, also capable of 868/915/2400/5600MHz.
So from with a combination of 433 and 868 Mhz modules, you can achieve your job. But this implies one thing.
The main arduino that will collect the datas must get 2 RF modules (one that deals with 433Mhz and one that deals with 868Mhz). So from an Arduino Mega will be the best choice as it gets 4 serial ports.
May be this way of doing things is not the most elegant but it can works.
Sure that people in this magnific forum will have other great ideas about your project.