Anyone have any ideas on what this part is called or where to find it? It did have a knob on the arm that allowed me to position the forward hatch for fresh air that opened up above the cabin.
I don't know if there's a technical name - I've always just called them the extension arm or support arm. Try googling for that - and keep in mind that you don't necessarily need the exact same style, especially if you're able to be a little creative with mounting options. But even without the creativity, it's quite possible that other "styles" will fit up just as well.
Can you find the manufacturer name on the hatch? GW used Bowmar in the past, but the rods are different from that (circular adjustment). You either need to find the manufacturer or google pics and see if you can match it up.