I think this would fit what you want in a way.
http://www.sinister-attraction.net/stories/a/prophecy.htmProphecy of Two, The
~ Author: Amanda K
Summary: In a world where vampires rule, Buffy finds herself powerless. Her single ally is Spike. Can she trust him to help her find their way home?
Here are the links to the other fics.
http://spikeluver.com/SpuffyRealm/viewstory.php?sid=17125Summary: Response to BSV challenge 157. AR When Spike loses in a high stakes poker game he ends up in a demon slave market, where a mysterious human girl purchases him.
http://bloodshedverse.com/stories.php?go=chapters&no=12604Goes AU after Life Serial. After Buffy is kidnapped by a horde of demons, Spike comes to her aid, only to find her imprisonment was worse than he could have imagined.