3 possible places, the 'ladder' is never in one fixed place, the items are; The roof piece, The ladder and The snow plow/Barge for the front of the bus.

The first possible location is the first room that you use the turbine to open at the bus depot, If you open the door it will be to your right.

The second location can be in the shed next to the mechanic workshop/Diner, There will be a tool shed/Barn, you will open the room with the turbine and it will be in the corner (back left) of the room.

The second location is the barn in the farm area/Sub-map, If you walk straight forward when you open the gate, You will see a tractor, Just walk past that and there is a barn that requires the turbine to open, The part will either be next to the tractor in the room/Barn, or it will be on the floor next to the tractor.

The fourth and last possible location is in the town, It will be in the room where the Semtex grenades are in Survival, It again requires you to open it with the turbine, If you don't know where this room is, it is on the far side of Town, The part will be just in front of you.


Hope this helped.