For piggy back on a mount and scope like yours Bintel has a $35 mounting bracket
https://www.bintel.com.au/product/ce...t-nexstar-568/
A different way would be a tube ring with a 3/8 screw. But.. that would put a lot of additional kg on top of the tube far away from the balance centre. Maybe Bintel can advise which mounting option is best for the weight of your camera and lens.