ebay would have lots, as do other online clothing stores that sell movie/superhero merchandise, hot toppic may have them. other than that if you really want you could use a shirt you already have and get it customised to have the logo on there. there are lots of websites and shops were you can design your own t-shirts or get logod printed on them
You can go to this website station look. They will give you a good idea [link removed]
Hot Topic sells them.