I am looking for a site like CafePress.com or SpreadShirt.com, where I can upload designs, visitors can pay for products with those designs (like t-shirts and mugs), and the merch site produces the product and ships it to the customer, paying me a portion of their income. However, I want to make sure that if I direct a visitor to my designs on the merch site, either via a direct link in an article or by a redirect from a site I own, the visitor will only see my designs that I have uploaded. I don't want visitors searching through other artists' designs that are similar to mine.
Are there any sites that have a feature like this? I don't mind paying extra for it.
Note that I'll probably also create a website that only shows my designs, but I want the option to send customers to the merch site as well.