I presume you mean that your building components for missile PDC's on Earth for assembly on Mars.
The reason your not finding an order for freighters to move missiles is that they can't. Aurora require magazine space not cargo space for ordinance.
What you want in game terms is a collier. In Aurora a collier is a ship with magazines that is a designated ammo resupply point. Configure the class loadout for the missile types you wish to transport. Then you can "Load Ordnance from Colony" at Earth and "Provide Ordnance Reload for" at Mars once the first PDC is completed.
I tend to do this with a collier, but without the loadout changes. Just use the ordinance tap to load/unload the desired missiles.