Gitorious, the software that runs Gitorious.Org is Open Source and can be installed on your own server, and I'm pretty sure if you are willing to pay a decent price, someone would be willing to support it. Shortcut AS, for example, the company which hosts Gitorious.Org and was founded by Gitorious's original author and current lead developer Johan Sørensen, offers commercial support and customized installations both public and private.
And GitHub has a commercially supported product called GitHub:FI (Firewall Install).
