http://community.wizards.com/forum/dark-sun/threads/1016611 in which Brian (screen name zombiegleemax) attempts to fill in the rest of the world of Athas from maps provided in the published setting. Here's what is mapped in the published setting:
Here's what it looks like on the fan built Continent map (maps 1, 2 and bits of 3 and 4):
And here's what that continent looks like on the entire world:
As you can see Brian had plenty to work with, Here's a thumbnail composite of the maps he got done before trolling and real life shut him down:
Full size maps as well as the photoshop brushes (just in case someone wants to pick up the torch) Brian used to make them can be fouund at the Athasian Cartographers Guild (http://ds.daegmorgan.net/).
P.S. I can't believe I missed this for nine years! (The fact that the Athasian Cartographers Guild was already in favorites indicates some awareness)