Can't seem to find door handle for this sliding glass door

Your door's mortise lock looks like it might be something akin to our 82-238 or 82-268B, in which case you should be able to use our 82-080 or 82-081 Handle Sets with this door. These handle sets have hole spacing of 4-15/16", center-to-center, so please confirm that would work for your door's mounting holes. 

Let me clarify. Mortise locks aren't a brand; that's the type of lock any patio door with an internal locking mechanism uses. So Milgard doors often use mortise locks like the 82-238 or 82-268B (they also often use the handle sets 82-080 or 82-081). Apologies for any confusion.