Wish I had a source of nice quality slate here. I do know of some fair slate deposits, that are nowhere as uniform as what you are showing, but would do for most of my applications. Unfortunately, those deposits are now within the confines of the greatly expanded Death Valley National Park, and so are off limits to collection, as I'm not willing to risk jail time and fines to support my hobby .... ;c)
Relatively large irregular sheets can be used en echelon as narrow scene dividers, as well as to form walls around tree bases and the like, to control slope shifting and watering from effecting trackage. A thousand and one potential uses really, so thanks for the tutorial on using it for structural detailing as well.