Thanks for your question. Unfortunately, we are not able to redistribute arcgisbinding via CRAN because CRAN has specific policies for redistribution of binary packages which this package is unable to meet, namely that it only runs on Windows, and its compilation couldn't be performed within the CRAN infrastructure.
We continue to host the r.arcgis.com repository which has compatible packages, and older releases are available via GitHub.
Cheers, Shaun