Why are you considering replacing them? Working inside a car door is a pain-in-the- @$$ Not enough room to see what you're doin' and too many dang parts in the way.
However, it is also one of the better places for a beginner to cut his teeth. Minor errors go unnoticed, and the car will still run no matter how bad of a job you do. The worst problem I've ever had was getting the correct replacement plastic anchors for the door panel.
You can buy as much, or as little as you want to from your local salvage yard. How many keys do you wanna have on your key ring? Unless you're a lock rebuilding expert, the "new" lock won't be keyed the same as the old.
Are your locks simply frozen? Or, are you sure they are broken? Do you know how to remove the interior door panel?