I bought one of the very first sets of headlight glass from bierhanzel, they are as real as i can find compared to any OEM lamp i have looked at.
they are a strange glass though, i am thinking they are not tempered in any way, as when i made moulds of the glass, areas that had exposure stuck to my material and when i separated them the glass flaked off... so, not borosilicate and not tempered, they also have cold flow patterns in them suggesting temperature issues when pressed... as they also have seams along the edges...
i would suggest injection moulding of UV protected poly carbonate... i have also been looking into this, but until i have a new part in my hand i will continue searching.