The RB1 DLC is still there just in an annoying place. Search Rock Band> click on Rock Band> add-ons The new store is tons better than the previous, which i could barely read it was that bad. The only thing missing is the RB1 Export Key, i can still get it from my download list, not in the store where it should say purchased
Bring it to the attention of the PS store support, not Hmx. They dont control how the PS store is displayed. All Sony has to do is add in the missing items and a Rock Band menu for old content.