Depends on where you are routing the wires.
If you are going through the outside walls,,, You may wish to visit an RV store as they have the one you need.
If you are going to terminate in a compartment Then Lowes, Home Depot, and many hardware stores will have what you need.
I do not think Radio Shack (normally) Carries the housing you need, the connector yes, but the plate it mounts in no. But most of the better hardwares will have that. for compartmnt mount, (or in a compartment you can just put a ground block, RS has that)
if mounting in a wall, Camping/rv store.