Dart 68 ceiling bows

Hi, in my Dart 1968 2dr HT, I've replaced headliners, with the bows (5pcs), but looks like I have no "adapter" or bracket because the holes in the body to mount these bows are not round, it's rectangle ones.

Not sure but looks like this is the detail in the left side in the center of the picture attached.

Question number one - where to get these ones? or does it have the name or part number?

thanks in advance, Pavel.