These guys sell all kninds of shielding material and have some general info on their site also.
There is a material called TI shielding. You can get it from Percy Audio.
I've used it between components (particularly my tube phono stage which is highly susceptible to noise and interference). It works well. It's kind of expensive. Some other people might have some cheaper solutions. One word of caution, is magnetic shielding can be somewhat problematic, because the fields are not linear and can go around shielding. It depends on the strength of the magnet and it's spacing to the shielding. Speaker manufacturers have built appropriately shaped enclosures with appropriate distances around the magnet that nearly eliminates the field. Once you've figured it out for a particular magnet it's easy to do--but might take some experimentation the first go around.
Some (most?) shielded speakers are not actually shielded due to the afore mentioned difficulties in constructing an effective magnetic shield. The trick is to take an additional magnet of equal strength and align it in the cabinet so the magnetic lines of flux from the speaker magnet flow to the second magnet and are more or less contained.
Bob Merrill from Underground Sound in Memphis made a shelving system consisting of very heavy metal shelves that he claimed provided the component shielding you desire. Last I checked he had a few left at very reasonable closeout prices.
My room width is similar to yours, and my solution is the easiest. Try the sub between your front speakers and in front of the TV. That's the way many theater set-ups do it. My sub fires to the front. Just put it about 3 or so feet in front of the TV. Your front speakers should be wide enough apart to accomodate this set-up. My sub actually sounds best in my room this way. Don't worry about mucking up any image stuff between your front speakers, they should sound just fine. BTW I have B&W matrix 804's.