David, I haven't seen an exact replacement for the light or lens, but I also have one broken lens and both of my lights have been knocked off their pegs many times. They are so loose now that I just drop them back into place. My latest solution is to remove the lights when I'm working around trees. I don't need lights when I'm far from any road.
Recently Spencer200 (a NH dealer) gave us a part number for a spring mounted breakaway light. Here is a quote from his post.
<font color="blue"> New Holland part number 86521841 break away flasher list price $38.42
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That might be a suitable substitute. I am going to look into that part, but I haven't done it yet.