There are numerous printing companies that will print your designs onto not just T-shirts, but also hoodies, hats, posters, cushions, bags, and phone cases, to name a few items. These businesses also offer fulfillment services. This means that you promote the merchandise on your own site and once you sell a product the printing company will not only print your design but also send the item directly to the buyer. So all you have to do is concentrate on the marketing and selling of your products, and the fulfillment company will take care of the rest.
Research individual companies in your desired niche: If possible, it’s always better to become an affiliate directly with a company (if they have an internal affiliate program), as no one else will be dipping into your commission rate. This is the preferred route for most of the prominent affiliate marketers, including Pat Flynn. Unfortunately, it’s also the most work, as you’ll have to do the research yourself to see who offers programs (they’re usually listed in the website footer).