Below are the direct download links for Windows Server 2019. Theses were initially pulled by Microsoft due to issues with the ISO's. These images should only be used in evaluation scenarios where you want to get a head start learning about the new features in Windows Server 2019. Do not use these images for production or situations in which system failure / corruption would be a concern.

Server 2019 Hyper-V
Server 2019 Datacenter (VHD)
Server 2019 Standard
Server 2019 Essentials