If it is an HTML site - you could use find, like so:
find $HOME/public_html -mtime +60 | mail -s "Files older than 60 days" email@domain.com
Details on different find options:
Find files by access, modification date under Linux or UNIX
If you're using a CMS, I'd recommend creating some sort of system to do the same thing with the content from the database.
A simple email with links to page the organization is reponsible for should work.
You could also get more sophisticated and issue the emails directly to the people that posted the content.
Good luck.