Czuch Chuckers: I don't think there is a "list" anywhere, but if you know the person, you can go to their profile, click on the "Stairs" page.

In the "Step (your/max)" column, if it shows like "-/2", that means they are on retirement from that stair. If nothing shows up, it means they quit the stairs (but just finishing up their current games). For example, in my profile - I'm retired from a few stairs like the the swap 5-in-line stairs and such.