You can buy US and Canadian stamps through USPS and Canada Post's websites. IRCs are no good in the US - many Post Offices don't know what to do with them since they're no longer being sold. (Plus it's a pain for the person or their assistant to redeem them - you want to make it easier for them to get your stuff back.)
Space enthusiast w/a Sharpie! Ex-journalist. Published in British Interplanetary Society's Spaceflight and National Geographic Traveler magazines; also NASA's Scientist-Astronauts, Freedom 7: The Historic Flight of Alan B. Shepard books and contributor to The Star Trek Encyclopedia: A Reference Guide to the Future and the A Matter of Time: The Unauthorized Back to the Future Lexicon among others. Follow me at @HBSastrowardoyo, check out my astronaut and other space travelers autograph collection at https://www.flickr.com/photos/45855752@ ... 973452526/