There are many articles for sale in amazon.ca site. Why can't PM advertise for sale their services and SIM card through amazon.ca. This will reach out to a much wider customer base and they can also manage the delivery of SIM cards on PM's behalf. However, I am not sure if CRTC would allow that.
Also, to save shipping costs, PM may also consider to have their customers to pick up the SIM cards from any Telus outlets. To avoid any impact on Telus customers, the stores will only be used for pickup for PM customers and will not sell any PM products.