These shirts are on sale at
MidwayUSA for $39.99 each thru the month of May. They are listed as "Elite 4-Pocket Discreet Short Sleeve Shirt" in 4 colors and 4 sizes, and are meant to be worn untucked.
The cut is generous, so you can order your normal size, and best of all, I think, the shirts are 100% cotton.
I bought one in dark green, shown here:
