Full disclosure: I'm the maintainer
In a number of (non-US, currently, though there are recurrant efforts in the US, too) jurisdictions, there is shorter-term, copyright-like protection for clothing design.
(Sorry but I almost never make puns but I had to make this one.)
> Ultimately, we decided on a full-print T-shirt printed on both sides, which was made for us by a local, friendly printing house.
The one interesting part, where to acquire fully printed t-shirts in Europe, was left out.
Refer to my top-level comment: https://news.ycombinator.com/item?id=16386307
Working link is: https://teonite.cupsell.com/