During the story you can only pick one of the three new contraptions. The other 2 contraptions can you find in the districts (chapters) so that you can get all 3 contraptions after the story. The Ramshackles can you find in the New Orleans Bienville Street District in the sewer and it is unmissable.
After you pick up the Ramshackles replay the Manhattan Harbor District after
you have killed the Übercommander here. At the beginning of ths district are 3 supersoldats. Kill the first one silenty activate the remaining two and run back. The supersoldat charging when enough space is between. When the supersoldat start his charge you see a fire on his back. If this happen sprint against him.