An indirect or direct TPMS is already installed during the manufacture of the vehicle. If the manufacturer should not install TPMS in the vehicle, retrofitting is not necessary, because then the vehicle is not subject to the TPMS obligation.
A workshop that offers the TPMS service can help you regarding spare parts such as a service kit for the valve maintenance or a replacement sensor.
Please note that due to the complex technology of the TPMS a specialist workshop, which has the appropriate speciality or programming tools, for tyre changes, maintenance work and in the event of problems (e.g. warning on the display) is to be recommended.