Windows Server 2019 Preview (the next major release of Windows Server) is now available for Azure Virtual Machine.
Just search for Windows Server 2019 when you create a new virtual machine
Search the marketplace (https://azuremarketplace.microsoft.com/en-us/marketplace/apps/) for Windows Server 2019
Or access the marketplace directly from this URL https://azuremarketplace.microsoft.com/en-us/marketplace/apps/microsoft-hyperv.rs5_preview
Enjoy 