I've never heard of Lombardi pines. Are you sure you don't mean Loblolly pines or maybe Leyland cypress. The cultivar 'Nana' would make a nice screen and only reaches about ten feet or so. Pinus taeda 'Nana'. Stay away from Lombardi poplars. They only live about ten to fifteen years here in Florida and they usually look terrible.
Some others suitable for screening are, 'Fastigiate' European hornbeam, Armstrong maple, "Fastigiata' Alder, and Fastigiate English oak.
Possible sources are:
Blair Nurseries
7480 S State Road 121
MacClenny, FL 32063
904-259-6281
Central Florida Lands/Timber
Rt1 Box 899
Mayo, FL 32066
904-294-1211
Superior Trees
PO Box 9325
Lee, FL 32059
850-971-5159
T&J Nursery
Rt # Box 153
Lake City, FL 32025
800-557-3806