Hi , I don't know where you're from but I'm french and I can grarantee you can find what you want in Paris. I wanted to be a mangaka too a few years ago, and now my little sister wants to work (and is already working) on drawing and coloring manhwas, so i know a few schools that are fine. First, you have "L'école des beaux arts", which is one of the best, but first, you won't be solely working on mangas, but also on modern art and everything, and second it's pretty hard to get in. There's also "L'école des gobelins" and many others (even outside of Paris), or you could do a "Classe préparaatoire" in art section (but careful with those, I don't think you can find classes in english and I did one in biology, i quit because it was too much stress and too competitive). Hope that helps.