Magnet URIs for SGS3 GT-I9300 UK and Brazil 4.3 Firmwares...
I got fed up with repeated failed attempts at attempting to download from TeraFiles or other such life/time-sucking/wasting distribution mechanisms. Managed to get a hold of the two files above, so Torrent away!
P.S. Wanted to give source links, but since I'm "new", I can't post links to Sammy Firmware.