where can i get the defult scenery for LHR/EGLL?

hi everyone,
After downloading scenery twice for LHR(EGLL), i have noticed that my frame rates have dramatically been reduced from 30FPS to something like 5FPS around heathrow. so i have decided to get the defult scenery file back up to its original settings, but i dont want to reinstall FS because ive got so may aircraft and AI traffic add-ons, so i just want the defult heathrow folder which is usually here:
C:\Program Files\Microsoft Games\Flight Simulator 9\Scenery\Cities
all help is welcome, thanks