You can also look for prunus tomentosa.

They can be ordered at these places:

http://boughennurseries.com/small_fruit.htm

http://www.greenbarnnursery.ca/collections/cherries

http://www.pepiniereancestrale.com/

http://thehoneytreenursery.com/Fruit--and--Nut.php

There might be other places in the prairies selling them.

;)

there are 2 Boughen nurseries that mail order and have nankings, one in Nipawin Sask, and one in Manitoba. I think Tree time out of Alberta may also supply these