A ran a search on "Anal Fisting" and came back with Search results limited to 1000! I'm guessing that means not all of the stories listed there have both themes you request. They can be found here.
When I run a search specifically in the Anal category and try the keyword Fisting I get 6 stories. Fist pulls up 4. Some of them may be the same story. I didn't cross check.
As for me, personally, the thought of anal fisting scares me.