Lock mechanism broke inside door

You have an older style handle set that I don't think is made anymore, which would explain why you can't find it. The good news is that you should be able to use our 82-080 to replace it, which is a more modern version of your original. The only significant difference is that ours is a little skinnier, but it should still work the same way.

No worries! Two mortise locks commonly used with the 82-080 are our 82-238 and 82-268B. You would need to compare with your old lock to see which matches best.