Tom, I have had gunwales sent from manufacturers with shipments of
canoes with no charge. I've also made my own ash gunwales.

But the easiest solution yet was finding an outfitter shop (Blue
Mountain Outfitters in Marysville Pennsylvania) that stocks various
gunwales (and deck plates and everything else too).

Whereabouts do you live? Maybe someone can recommend a more-or-less
local to you outfitter that carries gunwales in stock.