I'd look through a lot of the postings already.
Check this out first:
mating fics (very similar to claim fics)
Then I would do a search on
Elysian Fields: Claim Fics or take a look at Coalitiongirl's list that is listed in the above link.
Now specifically you might want to try:
Beloved in Blood by Ameeya Rated NC-17And if you'd like please contact me about Kari Mouke. She has a few where Spike claims Buffy. I have all her stories in a zip folder, so I won't send just a few. BUT...they are all very good!
Check out
Bite Marks by mjawMaryperk her site (but appears to be down?) (She has stories with claiming/mating)
Jackofspikes has some stories too,
her siteStrawberry Fields by Ameeya Rated: NC-17 *Not finished but it fits your criteria!!!!* (Definitely good read so far!)