It seems to me that, if you know what kind of wood was used in the paddle, you might take measurements from it and build a reasonably similar replacement...

There are lots of places to find plans for paddles, so you may look for a similar plan, then modify it to suit.

Just a thought. I'm just starting to make some oars for a dinghy I've built, so it may be that I'm just in the mode...

Good luck. Hope someone who knows about reconditioning paddles can help you.