Any Post Season 7 fics where Buffy and Spike adopt a child because they can't have one (since Spike is still a vampire)? Maybe find an abandon child that they raise?

Mrs. Muir wrote the babies series which has Spuffy as adoptive parents. It's a really long series - I never finished it, but I do believe they end up having biological children, too.

I can't post the link since I'm not registered, but you'll find at her website When Buffy Smiles. It comes up in Google search.

The Baby Series by Mrs Muir

http://dark-solace.org/elysian/series.php?seriesid=28

Summary: Series of four epic fics covering the Babyverse. Spike is called away by Drusilla before he can meet Buffy at the Bronze in Tabula Rasa. He doesn't return to Sunnydale until after the fiasco of Xander and Anya's wedding. Things aren't the same as when he left town...especially Buffy.

It's a really long and really good series of fics. I don't remember all the adoption details though but I do recommend it on general principles.