Hello! I think we can help with this project. Before I suggest anything, though, I'd like a bit more information. That will ensure that we get you exactly the right parts for the job.
To start, can you tell me the distance between the two installation holes on the handle set, center-to-center?
Regarding the mortise, can you remove it from the door and show me a photo of it by itself?
Once I have those two data points, I'll do my best to find you a good replacement.
Gotcha, that's totally understandable! I think I can still give you a solid analysis.
So, we don't sell anything with a 4" hole spacing, but we do have a ton with 3-15/16", which is just a hair off. 3-15/16" is a fairly common size for patio doors like yours, so you may want to double check just to be safe. I think that may be what you're looking at.
If so, my top recommendation would be the 82-087 handle set. This matches the color of the original and its thumb lever/key lock are in the same position. If your hole spacing is 3-15/16" (center-to-center) then I think this will be a winner.
And the 82-087 just so happens to be compatible with the 82-265 mortise lock. There is a very good chance this is what you have now. Give it a look and see what you think!