The LHS can order it direct from SIG, or you can order from Aircraft Spruce Supply. There are a couple of other places as well. It may be that your LHS has had the Butyrate on hand for some time, and wants to unload it. Lean on him, and get him to order you a quart. This will more than do the waco. You will end up thinning it over and over again. Do not order dope thinner, Automotive lacquer thinner works just fine, and you can get it by the quart at your big box home improvement store cheaply.

Bill, AMA 4720
WACO Brotherhood #1