What wood are you looking for?
This length is pretty easy to find in cherry, ash, maple, walnut,...
Well, at least up here in Canada.
I don't mean to hijack your thread, but title fits perfectly with the related challenge I was about to post ie. where to find 17ft quarter sawn oak for a circa 1900 Canadian Canoe Company vertical rib canoe. I will need white oak for outwales and keel, wide (single piece) butternut for decks. The original (?) maple seats are salvageable. The oak thwart is fine, and I already have thin stock (also oak) to replace the coaming.