Belden's website has a tool to find dealers. Markertek carries most of the Belden line and has their own 4-conductor 14 ga cable. Of course, you could always run two separate runs of standard two-conductor speaker cable. I ran 10 separate 12ga two-conductor cables through the walls in my theater to be able to put speakers where desired.
I found an even better Belden distributor: http://www.josephelectronics.com/
The guy I talked to was very helpful and spent quite a bit of time with me and made me feel that I was an important customer, even with my fairly small order.