Why do you need it to be in town? You can get these cables for dirt cheap online with free shipping. $10-$16 shipped.
http://www.dealextreme.com/p/usb-2-0...-capture-49146
http://www.dealextreme.com/p/easycap...e-dongle-11267
http://www.dealextreme.com/p/usb-2-0...er-black-51244
http://www.dealextreme.com/p/usb-2-0...ed-white-51347
Most of the time you will never ever find them in any actual store in Calgary or Edmonton.
Even if you do, expect to get heavily ripped off on anything cable related.
It might be a good idea to just buy a TV tuner that is on sale or on the red table at Futureshop. I got a Hauppage USB tuner (with coax that also works for HD) that will work with an SD VCR or HD source for like $40 on the discount open box table at futureshop.
I doubt you'll find an RCA to USB cable but most stores will carry TV Tuners for PCs.