Chilly,
As I understand it, there are custom t-shirt services springing up all over now. They take advanced orders so there is no waste, and only need 25 (?) orders to get the costs of the endeavor covered before they start making a profit. They create a design, then market it on Facebook, where they have access to potential buyers that probably have a genuine passion for the subject (via Facebook's demographic-marketing capabilities). Once they get 25 orders, the shirts are made and the orders are filled and sent out. They market the shirts as "limited editions."
The surface interval t-shirt is the first one that was pitched to me via Facebook on my newsfeed, and I liked it so much I signed up to buy one. It took a few weeks to get it (because they were gathering orders I suspect). I got to choose the style of t-shirt and the color I liked best (women's short-sleeve v-neck in navy blue for this one), which was really nice.
I have a friend who has created a limited edition t-shirt for his motorcycle racing hobby "shop" and used it to gather more fans for his racing efforts.
Puts a whole new spin on t-shirt collecting...haha!
Lidja