Here is one that I Found;
http://www.gillroys.com/Power_Tools/Propane_torches_and_accessories/Brazing_Rods-s315095.html
I believe you can also Buy it online from, ESAB, LINCOLN, I also see that you can order on-line from Grainger, just put in your search bar; Brazing rod for sale. Hope this helps.
Steve