Just how sure are you that a filter on the power line is what you need? What is the noise you are hearing?
I have several power line filters in my junk box and have never found the need for them. They have come from things like copy machines, PC monitors, printers, and such. Being small, they don't have a lot of inductance and probably attenuate best in the HF range.
Some power strips have filtering inside.
If you insist on a box to plug in, you could build one. Being a one-off you probably needn't worry about meeting electrical code requirements.