Good things often come in pairs:
Like these two made in USA blue Brooks Brothers button down oxfords, in my size, $9.98 for the pair.
In a down and dirty thrift store, if you find one Brooks Brothers shirt in your size, that obviously belonged to a guy who brought his shirts out to the cleaners every week, keep digging. Chances are there are more similar shirts in the same size, likely having belonged to the same fellow, who bought a dozen new in the 3 for $200 sale, then got rid of all those perfectly good old ones all in one fell swoop.
If you're especially lucky, his suits will be there too, also in your size.