If it's the cable end that came off:
I'm sure a new Brake cable is findable - do a little searching on the internet, ebay, or at a dealer.
Or - look in the yellow pages "cables" - there are lots of small businesses that specialize in cables. Take them your old cable and the old end, they can crimp on another one.
I doubt soldering will be able to hold it - there's alot of tension on the end when you apply the brake.
If it's the arm it hooks to that broke, a GOOD parts house (not Bubba and Yahoo's, not Autochina) should be able to order one.