You can search online and download the full installer for 10.11.3 (not just the combo update) and do a clean install, it is not directly from apple's servers and usually people don't recommend doing it since it might be a modified version (it might also be agains apple's terms and conditions).
The link you provided gives an expired version of 10.11.3 downloaded before Feb 14, 2016. There was briefly an updated version of it available between Feb 15 and March 20 and many who were unaware of this issue may not have redownloaded the newer version of 10.11.3 which now expires on February 7, 2023. On March 21, 10.11.3 was replaced by 10.11.4 and so the newer version of 10.11.3 can no longer be downloaded from apple.
Nevertheless you can still use the expired version:
If you are in the middle of an OS X install and get tripped up by the expired certificate you can work around the problem quickly as follows
1. In the OS X Installer, choose Utilities > Terminal.
2. Enter date 0201010116 and press Return.
3. Quit Terminal and continue the install.
That Terminal command sets your system date to 1 February 2016 -- before the certificate's expiration -- so the installer can continue. Once you have completed the installation, visit System Preferences > Date & Time to reset the system date.