Are you referring to the ones the students wear in the student section? Those were only given to student season ticket holders the past two seasons. This year, there was a completely different design for the student section t-shirt all together, so I don't know how accessible it is now. I've never seen them for sale in the Co-Op or anything. The only reason I have one is because my friend gave me hers at the end of the season
There are places you can take a picture or a .jpeg file and they will put it on a shirt, hat whatever you like.
Evenif it's from the internet? I thought that was considered public domain.
Sometimes they are -- but often there are disclaimers that say "don't use, mine" because the poster/hoster hasn't figured out how to watermark/prevent "borrowing."