The list of all ISO files, together with their SHA1 hash checksums, available for downloads on MSDN are as below:
To download Windows Update Version 1903 official ISO images from MSDN, you must be a MSDN subscribers or Visual Studio subscribers. Both Windows 10 and Windows Server version 1903 ISOs available for download on MSDN Portal’s Download section (previously MSDN Subscriber Downloads). Windows 10 OS Version 1903 has reached RTM milestone at build 18362.1, but the Windows Update v.1903 ISO images contain Windows 10 Build 18362.30, which mean the ISO has included the KB4497464 Cumulative Update. Microsoft has released the official ISO images of Windows 10 version 1903 RTM, publicly marketed as Windows Update, to subscribers of MSDN (Microsoft Developers Network), well ahead of public general availability scheduled on late May.