rothchild is wantingcameras/sensor modules for liberty prime
what places have them?

I keep all my sensor modules to make those badass bottlecap mines. Those things make frag mines look like firecrackers.

You can find a couple in the broken bow of the Rivet City ship though you may have to nick them from the facelift cat down there.

follow the link for the locations

sensor modules:
http://fallout.wikia.com/wiki/Sensor_Module

best place to look: somewhere mechanic, like RobCo facility, and The Mechanist's hideout

camera's:
random loot, although I found 2 of them in the back of the super duper market, also