Luculele:
The dissertation is in French and, as such, I can only really use French language sources.
To be frank, that sounds a bit odd. Can't exactly see how or why the language you write should limit the source material you can use?
Luculele:
I will be discussing three books in particular - Tintin in the Congo, The Blue Lotus and King Ottokar's Sceptre. I plan on addressing the racism question in Congo, Hergé's change of style and method in Blue Lotus and his representation of the rise of dictatorships in Europe in Sceptre.
That sounds like three different topics. Not much of help, but out of curiosity: how are you planning to combine the three and fit them into one thesis?
There was a similar thread recently which might help you out a bit:
https://www.tintinologist.org/forums/index.php?action=vthread&forum=8&t opic=3662.
But since you're fluent in French, you shouldn't have problems finding the source material. Unfortunately my French is next to useless, so can't offer much advice (However, I'd assume that searching the databases of national libraries of Belgium & France should give you a good idea what's available).
Oh, and I'd appreciate if you could post your literature list when you're done, would be interesting to see. Good luck with your work!