There are many online sources. I've bought fingerling potatoes from Potato Garden and Jung Seeds. They are fairly expensive because of the shipping, but you can be confident they are disease free. I've also planted organic fingerlings I got from the grocery store. In spite of the advice not to do that, I had my best harvest with the grocery store potatoes. I got close to 20 pounds of potatoes for each pound of Russian banana potatoes I planted.

There's a farmers market out by I-95 on the north side of Melborne I believe. I got my French fingerlings from Fresh Market...did great. If your hands are full of arthritis, fingerlings are difficult to hold on to while scrubbing and preparing to cook. French fingerlings are a little bit thicker around and easier to grasp. Check with your extentsion agent for best time to plant. In the meantime you can start working the plot where you're going to put them. Potatoes like an acid soil so you need to consider that.