Last it came up talking to Steph, she explained that Day9tv apparel including items that use the DayKnight logo are required to go through Jinx, so it's not quite as simple as sending to a print-on-demand service. However, it is still possible with the requisite amount of coordination.

I suspect the day9tv folks would ask the same question: how many people would be interested in either some of the day9 or dayKnight designs on sweatshirts? --> http://strawpoll.me/5741884