casement window operator assembly

I am having difficulty finding a replacement for a broken casement window operator. Attached is a picture of the broken operator. It has a flat arm that measures 9.5 inches long. The outer screw attachment holes are 3 inches apart. As you can see the wheel at the end of the arm is a flat metal roller. And the housing itself is 4 inches in width. Please let me know what part I would need to order to replace this broken part.

Thank you
Dan