Hello:
You may wish to consider purchasing one of the Playsims Publishing VFR Photographic Scenery Generation X packages:
VFR Photo Scenery - Volume 4 Scotland : The Western Isles (PC DVD)
https://www.amazon.co.uk/VFR-Photo-Scenery-Scotland-Western/dp/B0036PVBHM
Certainly it is also possible to make your own terrain mesh and custom photo-realistic terrain textures, then annotate the textures with autogen objects for use on your own computer.
But for any anticipated commercial purpose, you may need to purchase a license to aerial imagery and elevation data to match or exceed the quality in the above payware product (which is AFAIK no longer in production, in part, due to overall limited sales volume).
If you wish to make this scenery area for yourself, you may wish to review this excellent tutorial on using SBuilderX to make a photo-realistic scenery of an island, which includes clearly explained and detailed steps for the exclusion of default water polygons and creation of accurate replacement scenery content:
How to create photoreal scenery for FSX - by "Tiberius K."
http://www.flightsim.com/vbfs/showthread.php?250762-How-to-create-photoreal-scenery-for-FSX
A preceding thread apparently compelled
Tiberius Kowalski (aka "Tiberius K." at flightsim.com) to create the above tutorial, points out common errors which can be made when making islands (
ex: by incorrect use of Excludes, as well as failure to remove default CVX BGLs local to the area of an island and replace them with custom water polygons and other required content); that thread is here:
http://www.flightsim.com/vbfs/showthread.php?245629-Project-Nauru-PHOTOREAL-(in-progress)/page3
Note: The terrain resolution in the above linked Playsims Publishing VFR Photographic Scenery Generation X packages was reportedly a much higher 5 Meter resolution; the aerial imagery resolution was reportedly 60 cm.
BTW: A history of that UK photo-realistic scenery series:
http://www.arm-computers.co.uk/Photo_Scenery/photo_scenery.html
PS: Creating terrain mesh BGLs for that area would likely be limited to publicly and freely available 30 Meter resolution SRTM version 3 elevation source data.
Reportedly, most of the world areas publicly accessible as elevation data from the SRTMv3 data set have already been made freely available as ready-to-use 30 Meter terrain mesh BGLs:
http://www.avsim.com/topic/467933-freemesh-x-global-10-release-announcement/
Hope this helps with considering your options !
GaryGB