If you really want to sell t-shirts. Why not put a list of all active players on the back? I think most people will be 10x more likely to want one if their name is on it.
Personally I'm unlikely to buy one anyway, however I'm definately not paying to wear around a list of the gow gay club's circle-jerk champs. I know you guys are all pretty awesome so if you just want to make some shirts for yourselves, then gl and hf, but I wouldnt expect too many orders from other people.
Just saying, with love and apologies...
EDIT:
OK, re-reading that I probably could have explained my point a bit better:
If you want to sell T-Shirts, even if not for profit, then your primary customer group is going to be the people who are still actively playing the game. As mentioned, i believe most people would be far more likely to get a shirt if their name is on it. This is going to be the most effective way to circulate the most shirts.
ALSO: As advertizing for the server (and the game), I think it would be effective to have a larger list of account names on the back, perhaps with a title of "2017 top players" or something, and the server address. Then a list of the most used accounts from this year... maybe the top 30 or 40 or whatever... as many as you can fit.
Then when people see the shirt, they get the message that there is a large group of people still playing WC2 at war2.ru in 2017.
This is going to be the most effective way of using the shirt to raise the profile of the game and bring in new players.... if that is what you want from the shirt - but if a sub-set of people just want to produce a shirt for their WC2 group, well that's fair enough and I'm sure it will be a cool thing.