In general, you can expect to be able to buy cheap and moderate wine in any city, and in most towns, down to a population of just a few thousand. However, only in large cities will you be able to buy high quality wines, and only in very extraordinary wine shops would you be able to buy the finest of wines. Usually these very expensive wines are kept in bank vaults, and sold only to the very wealthy, and then only one bottle at a time.
In general, wines can only be grown on a large scale in temperate climates. For game purposes, that would be the areas on the world map in the second and fourth row of rectangles from the top. Locations known to the players would include Meest, coastal Attellaria, Calendriahn and the Free Islands, the Island Kingdom and Lyda, Dacia, northern Shintapoor (also known for rice wines), Graiwinor, and parts of Helghan, Islin, Goran and Dorwinion.
See the chart below for quality, prices and availability guides.