Italy and Germany both follow the FCI standard, which we know is not much different from the AKC standard. As far as conformation, very generally Italian Boxers seem to have pretty much the same strengths and weaknesses as German Boxers.
I don't know of any new German lines in the US, just the ones that have already been discussed.
I think you're going to have more luck finding the Boxers whose conformation, temperament and health appeals to you, without worrying about what country they're from.
American Bulldogs have the same roots as Boxers, most notably the old English Bulldogs, but they are a much newer breed (developed in the 1970s).