For a one off print, heat transfer or direct to garment printing are really your only options, neither of which are ideal in terms of quality/life. Most towns seem to have small print shops (printing “lads on tour” style shirts), one of them might be your best bet. Have a quick Google for local places. Then, I’d just source a good quality shirt and get them to print for you. I can personally recommend Continental shirts, they have a great line called Earth Positive.