We stayed at SSR in early January and we were able to purchase stamps at the resort gift shop, Artist's Palette. Check in the gift shop of your resort and you might be pleasantly surprised. I was quite prepared to pay a premium for purchasing stamps on WDW property, but they were face value. They didn't have the exact stamp to get the postcard to Canada -- but a combination of two stamps in their expandible file folder made up the cost. (about $0.60, I think)