Historically, RBN 2.0 songs were "Currently Unavailable" in the Rock Band Music Store external application, and they didn't show up in searches at Xbox.com.
There's a reason why I say "historically".
Thanks to some hard work at Microsoft, we've resolved both of these problems. All Rock Band Network songs are available for sale in the Rock Band Music Store now. You can also search for Rock Band Network songs on Xbox.com, so you can find every song by All That Remains* with one easy search.
We're always working to improve your Rock Band experience. If you run into any problems with this update, please reply to this thread and let us know. Thanks!
* Or whoever your favorite RBN/official DLC artist happens to be.