We at the Q&A service don't have info on which garden centers across the country sell which plants. Your best bet is to visit the following web site which will allow you to search for local garden centers carrying Monrovia plants. Then you can contact some and ask if they can get the type of lantana you want.
I should add however that in your zone 7 area lantanas are not going to be winter hardy, especially the above ground parts.
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