Answer: Blanket Flower will grow well in your gardening region, but may not have reached a level of popularity that the local nurseries want to stock it. You can ask them to order for you (Monrovia is a wholesale nursery and does not sell directly to the public), or you can order seeds through online catalogs. Local nurseries typically carry what grows well in the region and what is popular with their customers. However, if they order it for you they may discover others are interested as well.
Best wishes with your garden!
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