The carrier T-Mobile has released the Samsung Galaxy S10 5G for sale today (June 28, 2019). This coincides with its inaugural 5G service debut. However, it currently only covers 6 cities in the US, and not much of any of them at that.
https://www.notebookcheck.net/T-Mobile-switches-its-5G-service-on-now-sells-the-Samsung-Galaxy-S10-version-to-go-with-it.426690.0.html