There are only about 220 songs in the Rock Band Music Library that have pro upgrades so far. If you go into the Music Store and choose to filter by Rock Band Pro songs, it only takes a couple of pages to scroll through to see everything available.
Why can't I set my RB3 to start up with a pre-set filter so that I am only seeing pro songs? I dislike the extra steps after booting into the game, having to set my preferred sorting each and every time. Sometimes I don't want people to see non-pro songs in local play, even for a brief moment.