Just find a good quality Screen Printer and pay for Process Printing on a shirt. I work for a T'Shirt shop and we do Process jobs all the time. It's the best quality and lasts longer than DTG.
Thing is to find a good printer you can trust to get it right. We personally do mutiple tests of ever Process job we do to make sure the mixtures of ink are just right to get the print to match up as much as possible to the original artwork.
Only problem is that with that big of a shirt, a lot of things will look small on it. I wanna say we can print up to 15" wide by 20" tall, but I'm not sure. I'll check in the morning on our table sizes.