I wanted a t-shirt of quakelive for quite some time. After much shopping, didn't found anything, no store has them. So I made my own on spreadshirt.com (35$ with shipping). First t-shirt was just a bit too small and the image weren't red enough, more like red-brownish, so I made a new one and this is what it looks like now.
If anyone's interested in making their own, I'm also attaching the files I used, I modified them quite a bit and they have a transparent background so it fits any color but of course it looks much better on a black t-shirt
(just realized that quakelive forums modified my png image to gif, you'll need to edit them in GIMP to create a transparent background)