Most likely they are custom manufactured by the 1000's in overseas factories.
You could check the RN number on the label to research it though (or post it here).
When you say "quality", what are you looking for? To some that means "heavyweight", some that means "durable". Soft? Generously sized?
What are you looking for in t-shirt, specifically? That will help us narrow down some suggestions for you to try
:welcome: