Size-1 active sensor can be put on a space station, as can CIWS.
Also size-1 passive sensors. I've had good results from making small commercial scouts/monitors that can use size-1 sensors to sit on a JP or other important place and monitor space indefinitely.
Missiles can be put into a military "ship" that is nothing but MFC and box launcher and then carried in a commercial hangar that is part of a space station.
Note that commercial hangars will not maintain a military ship by themselves, so you probably also need a maintenance module in the design. And some MSP of course.