You're almost asking the impossible. Likely, the style of desk and the hardware is out of production. There is likely no reason for someone to keep parts for such furniture. You'll likely have to have it specially made, by a blacksmith or machinist. It wouldn't hurt to ask a local blacksmith.... that would be my best guess, as to who could fabricate a specific piece, as that.
Rather than that specific designed piece, is there an option for installing a different designed piece, that would accommodate the same function?
This's about the best help I can offer.