I went down the rabbit hole a bit with this shirt, and still I have no good information.
I spotted this Salvador Dalek shirt first on this Tumblr, and know what Doctor Who fans you guys are I decided to try and find out where to buy it.
The image looked like it was taken at a market or on a stall of some kind (based on the metal frame the shirts are stuck too), which didn’t give me much of a clue, but did make me feel a bit like Sherlock. I then Googled Salvador Dalek and came up with many worse shirts, until I came across this eBay auction selling the design with the seller claiming to have bought it at a British beer festival, it being too big for him, so he’s selling it.
I then went back to the original Tumblr and realised that the image was linked to Imgur, the popular photo service that was built by a Redditor and is used by many Redditors. This then led me back to the original thread on Reddit which was started by the person who took the picture, stating that it was seen at the Cambridge Beer Festival (where more than 100,000 pints were drank last week). Another commenter mentioned that they’d bought it at the Brighton Beer Festival last year, so I assume that means the sellers travel around different festivals selling shirts, which hopefully means that they might have a web presence of some kind.
Alas, that is where the trail ends, I could gain any more info about the name of the company selling them, so I’m throwing the net a bit wider and involving you guys on the off chance that one of you has seen the shirt being sold somewhere or know the designer/company.