Chris if you can’t get an original counterweight this is how I made one for my mount.
There is an extension shaft available (as in photo) if you want to order one and wait till it arrives.
Or go to a engineering shop and ask for a piece of round steel ( as in photo) have a hole drilled in one end and tap a (I think) 12mm thread and screw a bolt and loctite it in cut the head off.
Or you can just weld the bolt head on to the piece of steel if you can’t or don’t access to drilling and tapping a thread into the piece of steel.
https://hosting.photobucket.com/imag...2121D5DF6.jpeg
https://hosting.photobucket.com/imag...8FA173B2A.jpeg
https://hosting.photobucket.com/imag...A88E20982.jpeg
Alan