If you're buying trees rather than rooting cuttings, I would suggest:
Marseilles Black VS
Desert King (pot)
Verte aka Strawberry Verte aka Green Ischia*
Malta Black (pot)
Nero 600m (pot)
Ronde de Bordeaux (pot)
Most of these should be able to survive z7. Some might be better suited for pot culture only.
I have witnessed the roots of (*) survive over winter unprotected in Zone 6.
These can be had from:
Rabbit Ridge Nursery NC
Trees of Joy PA
Edible Landscaping VA
and the Dave Wilson Nursery affiliates (Sanhedrin; Raintree; Bay Laurel)
among other vendors