Anyone coming to this question that's using VS 2017 or later should be using vswhere to locate this file. @codingdave's comment is the closest but that still won't work on many computers.
I've added an example to the Microsoft Docs article feedback that shows how to do this with Powershell.
#the path to VSWhere.exe is always in programfiles(x86)
$progFilesx86Path = [System.Environment]::ExpandEnvironmentVariables("%programfiles(x86)%")
$vsWherePath = Join-Path $progFilesx86Path "\Microsoft Visual Studio\Installer\vswhere.exe"
# this tells vswhere to use paths of the latest version of visual studio installed
# to locate this exe anywhere in those paths, and return a single textual
# value (not a json object or xml payload)
$ttExe = & $vsWherePath -latest -find **\TextTransform.exe -format value
if (-Not(Test-Path $ttExe)){
throw "Could not locate TextTransform.exe"
}
#then to invoke a transformation
& "$ttExe" c:\Source\YourTransform.tt