Sliding door back panel on lock

Hello,

We'd be happy to help but it's tough to determine what you need without seeing the original part. It would help to see a photo of the mortise lock face plate, as well as the inside portion of the lock that engages with the mortise. Also do you happen to know the manufacturer of the door? Your photo reminds me of Andersen at first glance but we want to be sure before making any recommendations. Thank you.