Please help - Need sliding glass door Locking Mechanism

Thanks for posting. This setup looks a little unusual, but I am wondering if our 82-260 could do the trick. It has a similar recessed design to your old mortise lock. Compare the dimensions below to your old hardware and see if you think this matches what you need.

Alternate image for 82-260

Alternate view of 82-260

Our 82-260 does not come in white but the faceplate is removeable. So you should be able to swap them out with ease.