Throughout the game, you hear that trade in Dwemer artifacts and raw ebony, among other items, is banned/restricted by the Empire. Nevertheless, moon sugar & skooma are the only goods that are banned/restricted in any way.

Is there a mod that attaches a similar "no sell" script to these items, for the sake of realism?

I haven't heard of a mod that does this, but I like the idea. It shouldn't be too hard to make, especially with that sweet new service refusal filtering component of the MCP.

There's a few:
http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=7075
http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=6989
http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=7585