Hardware for a barn/sliding door that cantilevers into free space when open
Look for "full pull-out drawer sliders." Imagine the biggest drawer in a Snap-on giant tool chest. The big drawers ofter use 2 tandem sliders on each side of the drawer. There are ball-bearing models. Look for "architectural full pullout drawer slide." They can take the weight, but they might not have the travel distance. You could build a mechanism in this way: wall >first tandem slides >intermediate plate >second tandem slides >door. Build a vintage-look box cover over the mechanism.
Or you could look at truck/trailer manufacturers for sliding hardware.