You can get the ios6 GM versions (they will be identical to the actual released versions when they are released next week) through a simple google search
just click on the first result and you can download the gm from there.
(once you have downloaded, copy the .ipsw file from the disk image to your desktop, plug in your phone, select it in itunes and alt+click on the update button then browse to the ipsw file you just downloaded)