Clear cedar is available in the Northwest. I am just on the north side of the border and purchase my boards from small specialty mills that are willing to cut the boards the way I want them. You are not likley to go into a lumber outlet and just find perfectly clear, 20 foot boards. When you factor in the wastage on cutting around knots, scarfing, and the time (and money if you do not already have the equipment) it may be easier to purchase strips already pre-milled. Westwind does sell strips, but I not found their milling to not be that accurate and when they shipped some to me some time ago, they just threw them in a box. I spent quite a bit of time sorting out the strips like a game of pick-up sticks, resulting in damaged strips.

If you have to pay $10/bdft, then you are only about $100 less than pre-milled. Of course you could just drive up here and purchase strips, otherwise there is shipping, duties, brokerage fees on top of the $.50 per foot cost of strips. But many just want to cut their own as part of the total building experience.