Thank you to those who have reached out with offers to help. Very much appreciated.
A solution has been found, with neither the seller or I being aware that USPS conducts business in Canada! Their Flat Rate boxes make things easy (and cheap), and the seller has now altered all his listings to include International Shipping.
Earning Import Dollars for Canada's economy and depleting the West Coast of CMP parts. Has to be a good thing, eh?