Anyone ever seen any fics where Spike is a woman?
preferably canon compliant starting as early as S2

Bluemerlin

Over on AO3 the author lovelyorbent has a series of lesbian spuffy fics which you can find here. The first fic in the series, from what I remember, at least starts in season 2.

I don't know of any others that fit your specific preferences, but over on EF there is also:
The Man for the Job by lafillesauvage
«A new vamp cult is causing trouble on campus and Buffy needs Spike's help to bring them down. Problem is, he doesn't have quite the right...equipment. Luckily, there's a potion for that. S5 AU featuring a female Spike, a frustrated Buffy, and a flimsy excuse for getting the two to f....»
This one is short, fun, and hot.