Both Busycon carica & B. caniculata are very common in Delaware, Maryland,
and the Eastern Shore of Virginia (especially behind the barrier islands).
Just north of Norfolk on the "Delmarva Peninsula", there still is a company
that harvests these mollusks, cooks the meat, and exports it for
consumption.  Normal size of the shells is 6-10", with some much larger.
There is also a sinistral relative of B. carica, which is different in
shape, although quite similar, to B. contarium.  It is not very common, but
I have collected over 50 of these in the past five years.
 
If you decide to venture this far north, let me know.  I will give you some
more specific directions.
 
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Delaware