これを……

  _ground_obj as GameObject = null
  _ground as Ground = null
  ground_obj:
    get:
      _ground_obj = GameObject.Find('Ground') if _ground_obj == null
      return _ground_obj
  ground:
    get:
      _ground = ground_obj.GetComponent[of Ground]() if _ground == null
      return _ground

こんな？

class Accessor[of T(MonoBehaviour)]:
  _name as string
  _obj as GameObject = null
  _mono as T = null as T
  public def constructor(name as string):
    _name = name
  public obj:
    get:
      _obj = GameObject.Find(_name) if _obj == null
      return _obj
  public mono:
    get:
      _mono = obj.GetComponent[of T]() if _mono == null
      return _mono

class Thief(OreMonoBehaviour):
  ground = Accessor[of Ground]('Ground')

ポカミス修正