As of September 2019, Canadian pharmacies have been notified that they are no longer allowed by law to sell insulin to US residents except for emergency purposes. That means US residents can no longer cross the border and buy multiple boxes of Pens, Vials or cartridges. The pharmacies can only sell you 1 box as an emergency, even if you have a valid US prescription for more. I checked with several different pharmacy chains and they all gave me the same information. I guess this will kill the bus runs to Canada as well as individuals such as myself that were going to Canada to purchase insulin.
They did say that there were a few doctors (they were not allowed to release names) registered in both Canada and the US that could write a prescription to purchase a large quantity in Canada but I could not find one after calling at least a dozen doctors and clinics near the border. The last know one in my area recently passed away.