The Kingmaker AP (War of the River Kings) and Ultimate Campaign hardback both have Pathfinder's Mass Combat rules.
I am so glad that this thread isn't what my eyes mis-read the title as; "Large scat battle rules".
I thought the Warpath supplement was well done.
Not sure what your intentions are here, but my personal experience with large-scale battles in D&D/Pathfinder is that there are better game systems for doing that, and they can actually be combined with the RPG rules fairly easily. If you really want to do a large scale battle.
I once wrote my own wargame because we had some largescale battles going on in D&D and I didn't like the results.
But since then I've mostly stuck to the basic rules and set up specific encounters that had some outcome that would affect the larger battle. Take out the wizard raining death from his tower, or kidnap the enemy general, etc.