Harpers Garden Centre in Ancaster has typically carried both the controversa variegata and alternifolia argentea over the past several years, although I am not sure what they have right now. Vineland Nurseries has also carried them in the past. The alternifolia will fit into the space better, but can be finicky, whereas the controversa is robust. Although the controversa is striking growing in adequate space, I have seen pictures of them growing amongst other trees and against a wall and they still looked beautiful with confined growth. Since you are on a ravine, note that deer seem to love these trees and can destroy the beautiful shape, at least to the lower 5 feet, in one or two meals.