https://www.bleepingcomputer.com/news/microsoft/microsoft-finally-released-windows-10-redstone-5-iso-images-to-insiders/

Microsoft has finally released ISO images for a Windows 10 Redstone 5. If you’re part of the Windows Insider program and planning to test Windows 10 Redstone 5 from scratch, this should come as a good news for you. These ISOs allow Insiders to perform a clean install of Windows 10 Redstone 5 or skip straight to this build they are running an older version.

Currently the following Windows 10 builds are available for download from Microsoft's ISO page: