You can Google something like "made in America t-shirts" and should find plenty of results as I did (not trying to be a jerk and say "Google it", really just trying to be helpful if you are indeed looking). I'm not sure about the European Union.

There are quite a few but just an example: https://www.american-giant.com/pages/about-us (no affiliation or any further research other than identifying from a lengthy list of made-in-USA clothing).