Hmm. They do look like they're well used, meaning they probably work well.
Do you know if these are full tang? Meaning the metal extends inside the plastic all,the way down, or close to it?
IF these are full tang, you might check around for a woodworker. They would be your best bet to sculpt nice handles, and recommend that they try as closely as possible to keep to the same lines.
If they don't have full tang it will still be possible but I'm not sure the expense would be worth the results. There wouldn't be enough contact between wood and metal to keep them sturdy.