I think it tends to be harder to find black shirts in 100% cotton, but that may be just as well, since in my experience black cotton doesn't hold its color particularly well when laundered repeatedly over time.
Honestly, my best fitting RTW shirt (in the body) was a black Claiborne shirt from Macy's. The collar has shrunk to where I can't button it but it fits the rest of my body well. It was only like $30, so I can't complain.
I woud try H&M or Zara but there sites confuse me. Thanks for the links and suggestions. So would what im looking for be considered a 'Dress' shirt? I plan to where it casually with a pair of jeans untucked.
It's a dress shirt because of the construction and cloth. If it had buttons at the collar points it would be a button down. If you do find one, do plan to wash and iron it yourself, and do take out the stays in the collar before washing it.