Academic preferably...I've searched on Amazon but all the books on cagots have zero reviews...Saying that, I'd love enjoyable non academic books or even historical fiction on cagots for the fun of it too, I guess. Or even documentaries? I speak okayish French so French language would be okay and I have read L'Histoire des Cagots (Osmin Ricau) which I didn't find too useful...? Sorry for putting my wishlist on you all!
The only book I have ever read that referred in any length to the Cagots is "The Discovery of France" by Graham Robb (Picador, 2007). The book is about 400 pp. and has maybe 10 pages sprinkled throughout about the Cagots. FYI, on page 357 Robb refers to , "a little Cagot museum in the Pyrenean town on Arreau. . ."
Regrettably the cagots don't feature in historiography - French or otherwise - as there is no certainty as to their identity. The dominant hypothesis is that they were lepers who formed a community likely imposed upon them in the middle ages...as such I would suggest taking interest up in medieval lepers. However there are a few academic articles on the cagots from the turn of the 1900's which I can refer you to if you really want!