Do you intend to repair this, or literally replace it? If replace it with new, code would require you to do it to meet current requirements, and you cannot replace it with a 'like' item even if you can find one. You are allowed to repair what you have, though. Can't help with the brand or model, but depending on what's needed to repair it, it could be tough on something that old.
If you decide to replace it, they make what is called a remodel plate that would cover the holes from the existing handles to seal up that area, and a new valve would be installed in the middle.