What is the concentricity tolerance for an 11ga aluminum 8in tube from a standard and premium extrusion process?

It does not exist. Concentricity is the variation of the axis of one form to the axis of a datum or reference, it is a control of position. A single tube can not have a concentricity call out. You probably mean cylindricity which is a control on form. A quick google search yielded me such numbers as .015 inches, but it didn't reference the quality of the process. But I'm sure now that you know what your looking for you can find better information.