Q.Desert Willow tree
I am interested in planting some desert willow trees but need to know a little more about them. I live in a semi-arid area in Eastern/Central Washington, Cle Elum, where I have hot and dry summers, but snow and low temperatures in the winter. My soil is a clay type. Related to this I wonder about the problem of deer browse. Can you provide these trees if they might be suitable for my location? If not, where might I purchase? This same question applies to the Afghan Pine.

If your temperatures dip below 10 degrees F a Desert Willow Tree would likely freeze.
Here is a link with more information.
https://www.gardeningknowhow.com/ornamental/trees/desert-willow/caring-for-desert-willow-trees.htm
The Afghan Pine has a hardiness rating down to -10 degrees F.