Sargent & Co Easy Spring mortise lock

I'm not sure if we have a good match for this old mortise. That said, it reminds me of the one that comes with our 40-119 heavy duty knob set. Could this potentially work for you? Look it over and let me know what you think.

That's good news! I have a feeling that this might be really hard to come by, so the more years you can add to its lifespan, the better. Let us know if you ever need anything else, we will do our best to assist.