850Mhz support

Hi everyone, I am fairly new to OsmocomBB. Been in North America I acquired a C118(850Mhz/1900Mhz version of the C123) and a C156(850Mhz / 1900mhz version of the C155) but from what I understand at this point is that only 900Mhz and 1800Mhz are supported. I am trying to figure out what modification I need to do in order to implement North American support for OsmocomBB, do I need to modify the firmware or do I only need to modify the host application? Any pointer would be greatly appreciated. I tried to modify the host application but I didn't had any success so far... Also I am trying to acquire a C123 and I find it quite difficult to find in North America, anyone know where I could acquire it from? I have look online but I could only find it on https://www.samstores.com/ and it seem a bit pricey and I have no idea if this store is trust worthy. I am also interested to acquire a BTS for OpenBSC(I currently have OpenBTS running on my USRP) so if you have any pointer on how I could acquire one, let me know. Thanks, Hugo