I love this pairing, but it can be hard to find any good fics of the two of them T_T;;
I did find some really nice fan art pages in Japanese though!
Here they are! :)
Some of the art & comics in these links are NSFW!
This artist is excellent! Just check out her comics! I love the front page image!
http://houoku.web.fc2.com/index/pict.html (the 3rd pic is adorable) Kayo is welcoming Kusuriuri home (they are married..in her pic anywayz)
A few more:
http://takio.mikosi.com/mononokeroom.html (last pic in illust = *drool*....it's quite pervy) :D~~~~~
http://genom.lomo.jp/top.html (lots of cute KxK comics and stuff)
http://members.jcom.home.ne.jp/f-a/edesu2.htm (the 5th CG is awesome!!)
http://phw.tank.jp/zakki.cgi (Lots of KxK art & comics in this artist's blog, up to page 14)
http://foolfoolfool.bake-neko.net/framepage-illust.html ( Has some sweet but sad comics & illust featuring the pair)