I found this great site selling all kinds of retro-style t-shirts! You name it - they have it! Back To The Future, zombies, TV tie-ins, Keep Calms - you could be happy for hours just browsing!
Yesterday I saw on FB that they're running a giveaway for a free tee. You can enter right here: https://www.facebook.com/creamtees/app_228910107186452
It's a simple Rafflecopter entry with lots of options to win - the only problem you'll have is deciding what tee to choose!I'm eyeing up a zombie one but I also love this one which is of course from Back to the Future: