Archived - iTunes: How to prevent access to the iTunes Store on your network
Network administrators can block access to the iTunes Store.
iTunes, iTunes Store
To prevent client computers from connecting to the iTunes Store, network administrators can block the Internet host "itunes.apple.com" .
This also prevents access to the Podcast directory on the iTunes Store, but does not prevent users from accessing podcasts using the Subscribe to Podcasts option in the Advanced menu or from accessing podcasts linked on webpages.