The link from Apple's support page redirects to the Mac App Store but upon clicking download you're met with an error message saying you "This version of OS X can't be installed on the computer" Note: I've tried 4 different MacBook Pro TouchBar but none will download it. I'm only looking to download El Capitan so I can create a USB installer for an older Mac.
I was able to over come this issue by creating a recovery partition on a USB stick and booting up the old Mac using this USB stick and installing and old version of OS X on the 2011 MacBook Pro Here’s where to create the Recovery Disk from Recovery Disk Assistant
Macs use a different boot medium than HP/Dell/Lenovo/etc BIOS. This boot chip technology knows the minimum OSX it can run and cannot run or apparently even download an earlier version.
Apple support can sometimes give a special download code to bypass normal limitations.
Also, the AppStore will only keep the current OSX for ready download, unless you downloaded an earlier version while it was still available. If you did download it whie it was current it is under the "previous purchases" menu option.