It took me a couple weeks, but I found it.
It's called beurre de cacahuète here It took me forever to figure out what the word for "peanut" was. I don't think it's very widely consumed. I kept looking for it where the nutella and jams were (which seems familiar enough to American eyes at first glance), but apparently it's considered a foreign food, so I was finally able to find it between the Thai and Mexican shelves in the "Anglais" section along with mostly British foods. It feels a little sacrilege to smear it on a baguette but I keep doing it anyway.