My DH is 6 ft. 6 inches tall and weighs about 250#. He buys his button front, collared shirts(size 2XL tall) from Gander Mountain and Bass Pro Shop.
He has bought from the actual stores closest to us, but mostly he buys them online because of the more color choices.
They are nice shirts, and easy care: wash in the washer, and hang on hangars to dry, or sometimes I dry them in the dryer on the low/knits setting. But since it's so hot where you're at, the shirts would take hardly any time to dry if you hang them on an outside clothes line.