You can put the NAPP T-shirt designs on ~any~ shirt you want and some of the shirts do offer larger sizes. For example: The "basic" T-shirt goes up to 4x, the "value" t-shirt goes up to 6x, and the "Basic American Apparel" goes up to 3x. There's also a size chart for each different style of shirt so you can get the exact measurements. =)
I will echo everyone else, I'm 6'7" and also a little on the big size. Would love to wear these shirts, but know that they will not cover. It would be great for me if you offered XXLT (Double X-large and Tall).
It's can't be that hard to find shirts for this, I'm even okay paying $2-3 more for the taller sizes. Please give us options.