- Install 7-Zip from https://www.7-zip.org/download.html
- Download lessmsi/Less MSIérables from https://github.com/activescott/lessmsi/releases
- Download the .NET Framework 4.0 Standalone Installer from https://www.microsoft.com/en-gb/download/details.aspx?id=17718
- Use 7-Zip to open the downloaded dotNetFx40_Full_x86_x64.exe from the previous step, extract the files netfx_Core_x64.msi and netFxCore.mzz to a temporary directory
- Use lessmsi to open netfx_Core_x64.msi, scroll down the file list and select regtlibv12.exe (the one with Component = regtlibv12_exe_amd64 for an x64 system, the other one for x86, or both if you need both) and click the "Extract" button
- Browse for and select the directory you want to extract the files to, click OK
- Et voila, you now have regtlibv12.exe!