I am a photographer and would like to know how would I go about hiring a specific cosplay model for a paid shoot?

I think the problem here is that you are assuming that cosplayers are models too.

Surprise!

It may be in the way you're asking. Do you have a portfolio of your work on line? Are you giving out that link to perspective models so that they can review your work? Are you supplying references to prove that you're not some kind of sexual predator?

What's the problem with hiring someone from Model Mayhem and putting them in a cosplay costume? Why do you need someone who's into cosplay? Is it the costume that they have? If so, rent one instead. You need a model which is to say someone who knows how to do posing in front of the camera. Someone who does cosplay won't know how to do that nearly as well as an actual model.

Your question is phrased as if there must always be a way to achieve the outcome you want, but this disregards the freedom of agency possessed by the other person. That's not a healthy mindset. You made an approach and now you should just leave it at that - the other person is entirely free to not respond.

Of course it's possible they didn't see your message, or perhaps they're considering it, but they might also prefer not to reply negatively - lots of people are uncomfortable saying "no". I've seen and heard some people complain about a lack of reply as if it's rude, but this seems an egotistical perspective to me. I say only an abusive reply to one polite request would be wrong. I don't consider not replying at all to be impolite. This other person didn't ask you to contact them, so why should they be burdened with an obligation to respond?

It is possible that she can only be contacted through an agent or agency.