ESSO Gas Stations can be found throughout the country but like with most gas stations buying stamps from them can be a little unreliable. I have messaged Esso headquarters to see if they have any information on the sale of postage stamps and got the following reply:
Thank-you for your email. In 2016, Imperial sold all of its remaining retail service stations across the country to a group of Esso branded fuel distributors including Alimentation Couche-Tard, 7-Eleven Canada, Parkland Fuel Corp., Harnois Groupe pétrolier and Wilson Fuel Co. Ltd. As a result, there are no longer any corporately owned Esso stations. While Imperial Oil currently supplies fuel to all Esso branded stations, we no longer are we responsible for the daily operation of the fuel and convenience stations.
In order to answer your inquiry, you would need to contact your local service station/convenience store as the answer may differ from location to location.
As you can see it pretty much boils down to luck of the draw. Each location is operated by a number of different fuel distributors so it is worth visiting or calling your local Esso gas station to see if they have any stamps in stock. Some may keep the stamps behind the counter so it can be difficult to tell if they sell them without asking.
Esso operates under a few different names now including Exxon, 7-Eleven and a number of individual service stations so check back to our gas station page to see more options.