Nothing i could find.
Some mods http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=8572 manage to pull off the expansion thing well, dealing with the lack of tilesets. You can actually do lots of stuff with the existing tilesets, ive mucked around with it before. Just that there isnt anything that can be used for external pieces
Definately a niche mod market out there fore Sil tilesets tho
*hint hint* for people who do that sort of thing