The Chicoms make DVD players that play all regions. You can buy them in Europe no problem but I don’t see them for sale in the US.
I think someone not too far back posted that if you have some basic soldering skills and a few discrete components (diodes or resistors) then you can modify most newer dvd players to play all regions. Stands to reason: most manufacturers are not willing to pay extra to manufacture at least four basic versions of a product merely to sell the exact same item in different countries. It is easiest to fab one basic board with selectable options for different builds.
I always meant to look at a few players to see what I could find but have not had the chance to do so as of yet.