You probably need to use the MPQ Editor. The campaign maps are stored inside the MPQ. If you have the latest patch, you can also edit the campaign maps through World Editor (they are located in the "Blizzard Campaign" section inside the program's "Open Document" window).
Side Note: Actually, the campaign map files for "Founding of Durotar" in the legacy builds of The Frozen Throne (before the Reforged came out) are in a different places. This is because TFT didn't ship with a complete campaign by the time the expansion was released, and instead it was released post-launch in one of the patches. The campaign map files for "Old Hatreds" and "A Blaze of Glory" were inside the "War3Patch.mpq". Legacy builds of the game stored all patch contents and changes inside that "War3Patch.mpq" file. In order to open the "War3Patch.mpq" file for legacy builds of your game, you probably need a correct listfile like
this one.