Where to find Cesium developers?

We are developing a web application for the construction industry using Cesium. As an adjunct to our main development efforts we are looking to spin up a side project focusing on truck logistics, and we are looking for capable Cesium developers who can assist us to put that together (in a way that doesn’t distract our core team).

Where is the best place to find Cesium devs? Here? Upwork?

You can try to find someones at Upwork.com or Fiverr.com.
For Upwork I think it would be some bit hard to find CesiumJS talents becuase the portion of CesiumJS job in the Upwork market is rather little that other kind of jobs.
For fivverr.com you can check the professional GIGs about CesiumJS.
Also you can try Linkedin.com and Github.
This is a professional CesiumJs developer who want to work on CesiumJS project.