I've searched all over and can't find any official Fallout t-shirts. Can anyone shed some light on this or am I stuck with the eBay knock-offs for good? Thank you

I don't know where you are, but I found this:-
http://shop.cafepress.co.uk/Fallout-3?cmp=knc--g--uk--hum--apparel--search-b--Fallout%203_merchandise&pid=3607873&utm_medium=cpc&utm_source=Google&utm_campaign=Humor%20Apparel%20Generic%20-%20UK&utm_content=search-b&utm_term=Fallout%203-merchandise&gclid=CMyvpfHm-6YCFYVjfAodsnS8GA

I assume these are officially licensed (maybe one of the moderators could comment).