I think there are quite a few companies that print t-shirts from designs you can upload. I went for the first one that appeared called Streetshirts to see what my oblique banner would look like. I was pleased with the quality of the shirts and how the design came out. I’m not convinced I put them in the right places. (woops -image problem)
These two (an ‘antique’ t-shirt and a long-slieved shirt came to about £35.