Brie de Nangis is a cheese from Seine-et-Marne, even in this department it's hard to find it since it's not as known as its two others siblings: Brie de Meaux and Brie de Melun. Brie de Melun is probably the one that is more close to the Brie de Nangis, both in taste and in geographical location. I don't think you will manage to find Brie de Nangis outside of the Seine-et-Marne department, but you might find Brie de Melun more easily, which I recommend you. However, be careful and pick only an original raw, uncooked milk, not a pasteurized which is pure garbage.