Sounds like a case of Mapper's Block.
If I may, maybe you could grab a piece of paper and a pencil, close your eyes, and let your pencil wander. There doesn't have to be anything definitive at first. Simply imagine the shores, the mountains, or whichever feature you feel most strongly about and let your hands mark it on the paper. Perhaps soaring along with the creatures of the air in your world, your hand will make note of certain things that you may not have realized were even there...
Offering a blank canvas to someone upon which to place the images of your mind may not result in a product that you watned, especially since there really isn't something for the artist to see. Making your own rudimentary map would go a long way to having someone else finish it for you, or just pretty it up a bit. At this point it isn't about what your skill level is as it is about getting the images in your mind's eye to paper.
The image doesn't have to be crisp, precise, exact, what have you, but it should probably be yours. Something that someone else makes isn't going to have the feel of the image in your mind's eye, the details that you've already put there, and may not be a suitable home for either the Numenorians nor the Khorviarans. By laying the groundwork, regardless of the level of artistic ability would go a long way to enabling someone else to fulfill your vision.
Just my two cents.