Use GeoWebCache or Tilecache to generate your tiles. The Process is called Seeding .. You need to be aware of the different file storage schemas ..
References:
Discussion on the Tilecache Disk Format
There is also this process Exporting and extracting the tiles from TileMill That may suit as well ..
With GeoWebCache, accessing the data store directly is problematic, but you should be able to build a script to pull the tiles without any load issues, it is very efficient.
Once you have your scripts in place, you can reseed and re-download your zip files to keep your app up to date.