Try
north west T shirts.
I used to work for them, they're a bit slack, so ring them to let them know you're placing an order otherwise it might take weeks for them to notice, and they might not have your size & colour in stock.
It's not sublimation printing though (that's for mugs and stuff), it's DTG, pretty much the same result as screen printing but without the screen.
Only advice is, you'll need a big image to get a good result. If you're thinking of blowing up a 500px picture, you'll be disappointed.