There is a spiral staircase kitbash:

http://www.worldworksgames.com/store/in ... ucts_id=66

Hope that helps,
Zephalo

Sad to say.... There really isn't one in a full fantasy set that I can think of.


However this may be exactly what you are looking for.

It's based off the textures for the original dungeonworks, which is currently Out of Print, but I think you can pick up the hex columns for this set .
(Please someone help me out with the second link.... I don't have access to my sets from this computer, so I can't confirm if the hex columns are in the kitbash or in the main Dungeonworks set.)

I think that will cover what you are looking for...

Edit: Doh Ninja'd by Zephalo

There's a stone one in Castles & Keeps. You'd have to build 4 of them with support to create a full rotation though.