I know this reply is a few months late, but I'm new
There are a few brands of contact probes - Faro was mentioned above, Romer is another common brand. The larger arms can loose accuracy. One company placed the arm on a linear rail so that it could reach further. You may find used arms around - but make sure to contact the manufacturer to check if all the software licenses are still valid.
Generally, people will just glue a few spheres on the vehicle and measure them; then move the arm to a different position and re-measure the spheres. The sphere centers can be used to transform the different arm positions to a common coordinate system.
Henry