Doors and Windows - Retrofit Mortise Lockset for Exterior Door?

I have an exterior door in my 1908 house that needs to have the lockset updated. Door is 36" wide, oak, 1-3/4" thick. It currently is set up for a mortise lockset (locked with skeleton key, more like an interior door lockset), with flat 2-1/4" x 7" plates on both sides of the door, with knobs set-screwed to a shaft going through the lockset.

Does any company sell a retrofit lockset, suitable for an exterior door, that would use the mortise in the door end and be similar in the plates on either side of the door?

I would like to keep the older look if possible, and not have to do a lot of rework to the door. Let me know if I need to provide more details.

Look up a good locksmith in your area. They often have old or rebuilt locks that will work. They are all different, so take the old lockset with you. A new lockset to fit the old mortise can start at about $350, and go up quickly to near $1000