I've captured update packages of Windows Phone 8 GDR3 build 8.0.10521.155 and build 8.0.10532.166 from update server yesterday, These files are all CAB files, including Language Packs and MainOS and EFIESP files. There are also the URLs there are accessed when the phone is searching for updates.
Windows Phone 8.1 update packages coming soon, currently capturing doesn't work on 8.1, if I connect to the proxy it stucks at 0%. But surely I will find a solution.
The download links are in the attached text files, just copy paste it in your browser and enjoy