By default, TMS files are located on the C drive in Documents\My Tableau Repository\Mapsources.
After installing Tableau Desktop, this directory is blank; however, the directory may be populated with any number of TMS files. Note that in order for a TMS file to become available after placing it in the Mapsources directory, Tableau must be restarted.
A good way to explore the various TMS options is via the Tableau.tms file located in the Program Files directory. The default location for the Tableau.tms file is C:\Program Files\Tableau\Tableau x.x\Mapsources.
The following TMS example is an abbreviated version of the Tableau.tms file.