Not sure what the Edmonton location of Terasen Waterworks might carry, but the Richmond outlet has a HUGE selection, like 20-30 times what Rona or Home Depot carry. Having trouble locating that 6 inch PVC valve or fitting, they'll have it ... and will that be slip or threaded !! (they have normal sizes as well ...)
Usually only open weekdays though, since they cater to the plumbing and irrigation profession (but will sell to individuals).
http://www.terasen.com/Waterworks/Default.htm
I got 1.5 inch unions for $10.50 plus tax in Richmond two weeks ago.