You can download the latest man-pages tarball here; older tarballs can be found here. The tarballs for the man-pages-1.* releases can be found here.
Using Git, you can obtain the very latest version of man-pages from the canonical git repository on kernel.org using the following command:
$ git clone https://git.kernel.org/pub/scm/docs/man-pages/man-pages
You can see what's recently been pushed to kernel.org via CGit: https://git.kernel.org/?p=docs/man-pages/man-pages.git.
Since the 2011 kernel.org outage, there is also a secondary Git repository at https://github.com/mkerrisk/man-pages. (Please don't send GitHub pull requests or report issues via the GitHub issue tracker. See here instead.)