That is a tough question, as startup advice out there is "look between your friends". This is the same as saying "sorry if you didn't go to a top CS college to have smart developers friends. There is nothing you can do". Sam Altman in his last startup class went as far as to say that non-tech people have no business founding a tech business, quoting "software people should found software companies, media eople should found media company". I found that a little bit sad to hear.

Anyway, my advice. Start with "freelance-as-a-test-to-CTO contract". But the secret is to find a developer who is not a freelancer. Freelancers already made their mind, they don't want to be a CTO, they will treat your contract as any other job, probably not even prioritize yours.

You must find a non-freelancer developer with an interest to start a start-up. Maybe a guy with a dayjob who needs the paycheck and can't afford to quit it, or some other who already failed in one or two of his own ideas. Or a young smart developer who is still lookong for his idea of a startup.

Finding the right profile, you must deal with the agreement the right way. You must convince the developer that your idea has the potencial to be big. You must value his time and pay a reasonable fee. I think the right one won't charge the top market he would if he was a freelancer. He must gain other thngs than money with the job. Learning mostly. Learning about a code, as he will build a software from scratch, probably learnng new tech. Also learning how a business is built. If it fails he must be better prepared to startup his own thing, for example. That is the hard thing to get with freelancers. They will accept your proposal only for the money. You will never know if they are really interested in being part of your business for real. This is become a 100% certainty if you are outsourcing to a software factory or remote freelance, so don't even consider about it.
I would start with an hourly fee, i think it is better for a test than a fulltime hire. Sometimes might be even irresponsible to hire a developer to such an only-idea startup. Too risky.

Hire the guy to make the MVP with an hourly fee. This way you will know if the guy is good, if you work well together, if you cmmunicate well. He will also know if it is something he wants to dive in. So this would be the freelancer as a test to CTO.

Now, actualy answering the qustion to where find it. I don't believe in startup events or regular networking for this. You hire the more outspken and available developer, not the right one. A good tip that worked for me is to keep an eye for this guys that show up at HN front page with a technical post or a Show HN. Rule out the very experient and famous developers who are regulars to HN front page. Search for the new, unknown guy who did something bright (HN upvotes are a great filter from tech guys for this). At the Show HN rule out the full formed startups, look, again, for the new, unknown guy who built something great as a side project.

If you have experience in the field, a good idea and money to fund (and a willingness to go to SV), i think you are in good position to attract the top talent that appear here.

Also, look for someone in "Who is hiring" Hn thread (definitely not at "Needs a freelancer?" thread).