Casement Window Split Arm Operator Replacement Parts

I have two casement windows in need of split arm operator replacement parts. I have one left opening window and one right opening window. I am looking for a complete set of hardware for both windows, including locking hardware, crank, crank handle, connecting arms and all locking mechanisms. Basically everything but the window. The only visible marking I see is a number located on the crank arm stamped 21550. I am also attaching photos and would like any help you can give me in identifying the parts I will need. I want to make sure I'm purchasing the correct hardware. I can't send pictures of it disassembled as it is part of my front bay window. I appreciate any help you can give me.

Lisa 

Hello! Thank you for responding with such excellent information. The dimensions in the numbers you provided above (39-317 and 39-318) are the same. I just wanted to ask if the difference in the numbers are right and left operators? I'm guessing they are but wanted to double check with you. As for the locking mechanism, that has been long broken but I am attaching a picture of what is left of the one we had. I appreciate your help and thank you again for your answers. As soon as I hear back, we will be ready to move forward with ordering and finally get these windows back to operating condition

Lisa