As a fellow tall, I don't even buy things unless they are "T" sized anymore. Gave up on it a long time ago. My shirt size is "XLT". There are sometimes things like work events or other places where they are giving away T shirts and they ask for my size and I tell them XLT and they are like "How about XXL?" and I'm like "No". I don't need to add another ill-fitting t shirt to the pile of shirts I will never wear.
Kohl's has a big and tall section that is pretty reliable. The past few years I have been stocking up on Tommy Bahama clothing. I have a relative who works pretty high up the chain for their corporate office so I am able to get a discount which brings the price of their clothing down from "outrageously expensive" to "still pretty expensive". It's damn good quality clothing though. I have the Big & Tall Bali Skyline T-shirt in every color. It's probably the most comfortable thing I have ever worn.