Sorry for the very late response; I don't get notifications about new discussions.

All maps use a script to tell TTT what weapons to spawn at the beginning of a round. When the mapper scripts what weapons to spawn, they normally only place the default TTT weapons, as they aren't expected to place weapons from custom addons (because not everybody uses them). The reason that they spawn on some maps is because the mapper placed a random weapon entity. This random entity will tell TTT to place a random weapon from all of the weapons that a server has installed, thus sometimes spawning one from this weapon pack.

I have an addon that lets you place weapons from this pack on to any maps you please, but it is a little broken right now and I am getting around to fixing it. However, if you follow the instructions in the description perfectly, it will work.