Mystery item broken on old Dawes. Help! I was adjusting rear brakes last night and this little thing snapped in half (see image [right]). The linear indent holds my brake cable in place and a 5mm bolt holds this in place. I guess I need to find a replacement but I have no idea where to start. Does anyone know what this might be called? Can I stillfind something like this?  

Bike: Old Dawes Horizon (1990's maybe?) 
Braking system: Centre pull cantilever. 

Thanks!
As the comment says, it is a cable clamp. They come in a variety of styles, knowing the make and type of brake it came from would help your LBS find something that should work.