To add a private channel get the code, and add it via your roku account. In roku account find add private channel link.
Private channel list can be found here....... http://www.roku-channels.com/home
Also private channel announcements are made in the forums as well.
Some private channels that are brand new you may have to PM the channel developer. which looks like the case for your desired request here.
See the sirius/xm thread for release notes below. I suggest reading through it all. Towards the end of thread you will see a second option for setting up the channel......... viewtopic.php?f=28&t=30812