Ken Blanton's recommendation is the first direct source I have seen in the immediate vicinity of SF. Farther afield, Jackel in Watsonville usually has clear cedar, but I have only seen it in 8/4 and larger. I'm not sure about really long pieces, however their stock changes and you could check before driving down. They are rather expensive, but do have some beautiful wood. They seem oriented toward architectural and cabinet uses and don't have any of the cheap siding kinds of things. You could combine a call there with a trip to Santa Cruz and/or Monterey.

Another alternative would be to try a weekend getaway to the Mendocino coast. I have found cedar siding in the local lumberyard in Fort Bragg, but only wanted a couple of smaller pieces for a project and don't remember pricing.

I don't understand why the cheap chains in the midwest seem to have stocks of cedar siding etc. and here on the west coast where the stuff grows (well, north of here anyway) it is so hard to find. Redwood is of course widely available and is useable for a stripper, but heavier and more problematic in use than cedar.