The Repair ship is not sold in retail freelancer but can be seen moving arround and mooring sometimes. In many mods where this ship is included, it has no weapons but alot of regenerative equipment (6-7 hundred shield batteries/nanobots), however this is not normally useful. Still, if you plan on getting a capitol ship you should get a repair ship first so the regenerative equipment transfers over to your capitol ship.
With the hazards of business, commerce, expansion, and exploration, ships sustain damage. These units are part of the damage control team.