In 2019, this is a quite recent link from Microsoft about how to obtain this tool:
The SignTool tool is a command-line tool that digitally signs files, verifies signatures in files, or time stamps files. For information about why signing files is important, see Introduction to Code Signing. The tool is installed in the \Bin folder of the Microsoft Windows Software Development Kit (SDK) installation path.
SignTool is available as part of the Windows SDK, which you can download from https://go.microsoft.com/fwlink/p/?linkid=84091.
I only needed signtool, so I chose the minimal I came up with and signtool.exe is now in C:\Program Files\Microsoft SDKs\Windows\v7.1\Bin\signtool.exe
Microsoft article link: https://docs.microsoft.com/en-us/windows/win32/seccrypto/signtool