Im not sure but there was a WWII Airborne mod on the Nexus. It included armor and a BAR+Springfield rifle. Its been deleted from the Nexus tough so it would require some digging to find it. Idk if i still have the mod somewhere. This guy has alot of WWII weapons (a few american one's) http://www.nexusmods.com/newvegas/users/7359888/?tb=mods&pUp=1
I don't really know what pack there could be. You might be able to port over the 20th century mod from Fallout 3 to new vegas.
Also here is a flamethrower from WWII-Vietnam War era http://www.nexusmods.com/newvegas/mods/42600/?
there where more WWII mods a few years ago but they got removed or something