I’ve used Howie’s Power-Vac http://www.howiespv.com/ to clean out my oil furnace ducts before. They’re out of Edmonds but service the greater Seattle area.
We used Howie’s to clean out our furnace heat exchangers and ducts (and dodge the bullet of a new furnace). They were great — less expensive than they predicted, quick, and friendly. And explained everything they did. Can’t recommend them enough!