Accelerando Studios has started a service which looks to help music makers bring their music and tracks to the Rock Band Network. Using their service, they will work with you in bringing your music more exposure by helping distribute them on the hugely popular Rock Band games using the new Rock Band Network service.
The pricing for the service is dependent on several factors but Accel promises to be reasonable and will work with you on a good price. A master track would be preferable but the group at Accel will work with you and do whatever it takes to get your music on the Network. Sounds like a very nice service provided to music makers who want their music on the Rock Band Network but do not want to deal with the technical aspects of it.