Yes, that lug came with the Bergara barrel. When I picked up the Bergara barrel they were more available, but now the selection is very limited. In fact, it was pretty accurate too! The two groups below were some I just guessed at, loaded and took to the range, not bad, considering the red diamonds are .5" square.
The only down side to the Bergara smooth nut is that it is installed with a plumber's strap wrench, so it's not possible to torque it to a consistent value, but then maybe that's not all that important given that it works well enough.