Edit: This has been solved. It is indeed once a week on 34 and 35, with an apparent showing factor of needing at least one Skolas completion.
-
You guys may accuse me of lying since I don't have video proof, but a friend, someone off the forums, and I did skolas today and after we killed him every single one of us got the elder cipher. That's right, it dropped for all of us. I don't know if that is extremely lucky or not or if it always happens like that but we were really happy