I found a post on another forum about Double Devon:
"The one I buy in Canada is called "English Double Devon Cream" and it's made by The Devon Cream Company, Corsham, England, SNI3 9XN. There is an e-mail address: firstname.lastname@example.org
I think we've just bought some of that (or similar) from Safeway?!
Have you tried the Farmers Markets in Calgary? If they don't make it already, perhaps they would give it a try if you mention it to them. (Not sure which stall though - maybe one of the home baking places?)
Otherwise, there are online shops that import it (e.g. amazon), or you could make your own version with heavy cream (noticed a few recipes on the internet when I googled).
On the plus side, think of the calories you're saving from not having it!