I love blackberry's and blackberry jam is my favorite. But I can never find fresh sweet tasting blackberry's here in Canada, don't know where they come from but they always have a sour bite to them, and I hate to put sugar on them to sweeten them up, because then they are no longer in their natural state. Blackberry's in Canada, at least in Vancouver are expenisve.
Try Costco, just got some last week in Kelowna, so you should be able to get them as well - imported from Mexico.