The more specific you are with what your story is about and what you need your coauthor to do, the more likely you will be able to find someone who's interested in helping out and well-suited to the role.
For instance, beyond just having a villain protagonist, what's the premise of your plot? Are they after revenge? On the run from the law? Is there some grand heist that they're planning? If you haven't figured it out yet, then I strongly advice you to come up with a clearer plot outline before recruiting someone.
How complicated does the scripting need to be? Is it really just tracking a few variables like money and key decisions, or will the game actually need something like a battle system and specialized items?
Ideally, you could also post a small sample of your writing, because a lot of people would prefer to co-author with someone who has a similar style.
