>>96917642
>Gifted or Purchased
Nothing short of recovering complete STC blueprints, and even then it'd probably be one that's sitting in the reserve fleet, not a front-line unit. More likely the RT is able to salvage one from a Space Hulk or as a derelict.
The problem is keeping it in fighting condition, which would require some significant logistical backbone to do - and you'd have to remain in good graces with the AdMech at all times in order to get a drydock large enough to accomodate it for regular maintenance and more complete repairs.