For any airports that you don't wish to model you can just define the runways and airport so that they show up on the maps. You should follow the tutorial specifically for this located in out wiki HERE
As for the UK, if you use the FSET tool you will be able to search the areas that you want. I believe that the UK is available to download but i'm not 100%. Be sure to also check out the FSET tutorial in the wiki as well to learn how to find and add your sceneries.
