Wasn't there an adventure or supplement for an old edition of Ars that had Simon Montfort and info on the Albigensian crusade in it?
Or is my memory of window shopping in a game store long gone only a hallucination?
My guess is the 3rd Edition Mistridge supplement, which was left in the possession of my ex, so I can't recollect, and I haven't bought it "back" from e23...
Mistridge does have a chapter on the Cathars including a bit about the Albigensian crusade, though a quick skim didn't give any headlines with Simon Montfort.
He might still be in the text though, it was just a quick skim.
I've checked my PDF of Mistridge. It does have info on the Cathars, but not Simon, which is what I remember most clearly.
Maybe I'm just crazy.
I know there is also some info in A Midsummer Night's Dream, but I'm not sure how extensive it is and if it includes Simon Montfort.
A friend of mine, Frederik J. Jensen, has created an Indie game called "Montsegur 1244" telling the story of the final days of the Cathars. It is in itself an incredible strong and passionate roleplay experience, particularly for players with an interest in story-based games in a historical setting, but it is also a wealth of inspiration that can easily be used in parallel stories in other games and Ars Magica especially.
This is no coincidence as I believe Frederik had been part of a long running Ars Magica saga focused on the Pyrenees and the Albigensian Crusade prior to conceptualising "Montsegur 1244" as a result of the impact the incredible story of the Cathars had had on him. Heck, he's been so inspired by it that he is know finishing the development of a board game about the siege.
Now, I know this isn't the canon Ars Magica you might have been looking for, but it is a quality game that is packed with ideas on how to transfer the historic events surrounding the Cathars to the medium of roleplay.
Not "Simon" but several bits of the 4e "Medieval Tapestry" book, particularly chapter IV, "Those who Pray," has Cathar/Albigensian stuff... 
Arnald-Amaury, Esclarmonde de Foix & the box-text "The Fortress Montsegur" look relevant, but my skim through didn't find Simon... 
1 Like