Well, it can be done pretty easy, through some HR agency or simply by picking up some reviews. Personally I would rather recommend to apply to Scand https://scand.com/hire-react-js-developers/. The thing is that React.js team offers a full-cycle development process, we ensure the delivery of ready-to-use, competitive, maintainable software solution. Believe me I know what I am talking about. They helped my firm a lot to become one of the most successful in the region. Hope it can help
To hire a good React.js developer for a project, you really have to look at their skills and knowledge. The candidate has to have experience working with React.js and be familiar with the latest trends regarding the newest releases. Also, you should request feedback from candidates' previous employers.
You can find good specialists in outsourcing but I would advise you to contact a development company. They will not only create a quality product but also take advantage of all the benefits of React JS. We were helped by Webspaceteam they have not only extensive experience in React JS but also have great further support and maintenance services.