I've been doing a bit of review and so far this what I've found:
Scene 2 of Rocco's Intimate Castings #2 with Christen Courtney and Chad Rockwell is anal only, but has an emphasis on sloppy BJs.
A lot of stuff at Asshole Fever is surprisingly anal only! From a somewhat "namebrand" studio this is actually super cool.
The beginning scene to All Internal #5 by Cruel Media is an anal only mini-gang with creampies.
Scene 5 of Fire in the Holes with Sarah Simon is an anal only threesome!
Megan Rain over at Hookup Hotshot has an anal only scene, but with an emphasis again on sloppy BJs and humiliation. The opening is pretty hot though with the two texting each other about how they only want to do it up the butt.
I think I'm gonna dig through some more scenes and see what other cool anal only things I can dig up. If you have any questions, just message me.