Miscanthus grows best during the summer. Local garden centers typically have them available late spring and through the summer.

One way to obtain what you want, is to contact a large local garden center and ask if, and when, those cultivars will be available. If the center won't be selling them, ask if they can order them for you.

Where are you located? With the exception of Mt. Washington, I have never heard of any of those cultivars and there seems to be virtually NO information on any of them online or via current OG resources. And none appear to be available or for sale in the US through any of the large mail order OG nurseries. Are they very new introductions? European introductions?

FWIW, Miscanthus sinensis is considered an invasive species across much of the eastern part of the US - that alone may limit the availability of any new to market cultivars unless sterile.