Craig,

I've check my hoard- most of them (including some that are almost black with age and carry) are labeled "US SPEAKER". Some are labeled "MIL-J 0387". The "Speakers" seem to be a tad better- looks like heavier plating, and they have a little more resistance to falling open, but they all lose the plating with pretty quickly and they all fall open and need to be taped or contained, so I wouln't worry about the difference. Both work fine.

The oldest-looking of them all is labeled "US G G GREENE 1956". It probably came out of a c-rat box in the '70s. It's pretty black, has seen a lot of use and carry, and still works fine.

I'd check surplus stores. I've seen them wrapped in brown paper, or loose. I wouldn't buy any that came in a retail bubble pack.