There aren't many of them:
In 0.22b (and older releases):
- Mary's is unlocked as part of the option to invite her to your room, after Chapter 1 has been cleared.
- In the Christmas Special 2022 (separate download), Leyla has at least one anal animation in her epilogue scene.
In 0.23 (not public yet):
- Jenna's is added to her regular dungeon sandbox options.
- Emily's third dream has a new option to put it in, if she's at Relationship 2.
- On the Carnal Crystal (unlocked after Jenna joins the mansion), there's an anal fantasy for Iris.
I might have missed one, but for the most part that's all right now. Kate will get one soon.