An obvious name to add is Ebbets Field Flannels (
www.ebbets.com), they make some outstanding hats and jerseys and all of them are made in the U.S.
Unfortunately, they don't have a license for MLB teams. They did however produce some of the best MLB replica hats for Mitchell & Ness, which are now highly sought after.
American Needle in my opinion are some of the worst replicas out there (they are made in Bangladesh as well) and lack any detail a true vintage replica cap should have.
The sad fact is, that at the current moment there are no high quality MLB replica hats available. The last company that produced a well made replica hat was Roman Pro, but they are long gone.