Moving this discussion to the Enterprise Deployment for Creative Cloud, Creative Suite forum.
Don the InDesign CS6 8.1 update is only available for Creative Cloud members. The last released perpetual version of InDesign CS6 for Mac OS is 8.0.3.419. For Windows the last release of the perpetual version of InDesign CS6 is 8.1.0.422. I apologize for the confusion.
The 8.0.3.419 update does not appear to be available online. If you fetch the update on a computer which can access the update server then the update will be available in the Temp directory. Another option would be to utilize the AUSST utility. You can find more details at Adobe Update server | Adobe Installation and Licensing.