It appears you were successful in finding that unusual screw that was left out of your shipment. I thought that it would be very difficult finding a a screw with those unusual threads.
Looks nice, I hope it works as well as it looks!
I have not found it. I did contact the supplier and they have already mailed out a replacement. The bracket is held on by one screw but is very stable. Since the wind impacts the bottom side first that is where the screw is.