I know you can find it in stream beds, and sometimes on the sides of cliffs. I haven't seen any in Vancouver yet though. Suggestions? It doesn't have to be overly pure as I'm making some bricks with it.
Talk to pottery people in the immediate area and use the Internet to look up Do-It-Yourself clay digging and cleaning and see if you can get close to Vancouver. Don't forget that some of those deposits are going to be on private property or on protected land.