I'm not sure if the government has owned any. However the US Capitol Building used slave labor, now there's a commemorative marker acknowledging it. According to this page:

Enslaved laborers, who were rented from their owners, were involved in almost every stage of construction. They cut trees, cleared grounds, baked bricks, and quarried stone and delivered it to the building site. They molded clay, sawed timber, and worked with masons to erect the building. In the early 1860s, an enslaved craftsman named Philip Reid assisted with casting the bronze Statue of Freedom on the Capitol dome