I doubt your Kindle International needs updating but if and when it does and you want to do it manually instead of using Whispernet, you can find the .bin file on
this page. If that U.S. site link doesn't work for you, search the Kindle help file on your country's Amazon site for "Kindle Software Updates".
My guess is that the Kindle Sprint and AT&T versions will probably always have different software versions because the hardware is slightly different (just as Kindle 1 and Kindle 2 U.S. do).
Please be careful, you don't want to brick your new Kindle.