A cobra head has a coax connector on one side, and a pair of thumb screws on the other side for attaching wire to. I don't have an NSN, but there's lots of them floating around in the system.
Any ol' coax will do, if I've got a few minutes later on, I'll cut one up and take some pictures.
There was a lovely little cartoon style publication on improvised antennas, I think I asked about it a few years ago here, and someone posted a PDF link.