It doesn't exist, yet. Creating scenery takes a lot of time, and I don't have the same amount of free time that I had in the past. However, if I ever get around to it, this is where you will find new scenery.
Most of the old FS2004 scenery still works in FSX to some degree. This is due to the fact that the SDK was strictly followed, and so the only parts which are "broken" are some specific elements of FSX which weren't made backwards compatible by Microsoft. What will probably happen in the future, is that I will reuse my FS2004 objects, and modify the airports I created in order to incorporate new FSX features.
In the meantime, try using the FS2004 scenery - most of it still works pretty good.