You probably won't be able to get any from anywhere, because it's a 'created' plant whose seeds will breed the original Greek basil. Best to buy a plant, and take cuttings from it now and then - that way, each plant will be a clone of its mother.

This plant, also known as 'Lesbos' or 'Aussie Sweetie', is known for its distinctive taste and growth habit, as well as for flowering rarely in our climate. Plants are readily available by mail.

See this post about the plant, and this one about propagation.

Just wanted to chime in here....I have Greek Columnar Basil, grown from a seedling. It's HUGE now, so beautiful. I love it. The smell is so aromatic. Very lemony, like sweet basil. It's a great plant.
One of my stalks broke off, and I took it indoors and put it in water, and before long roots sprouted, and after dipping in some root hormone, I transplanted it. It's doing really well inside the house.
This is a great basil.

Steve, what's it taste like? How do you like it for pesto, tomato sauce, etc.?