From "far away" vineyards, evidently.
There stood barrels, and barrels, and barrels; for the Wood-elves, andespecially their king, were very fond of wine, though no vines grew inthose parts. The wine, and other goods, were brought from far away,from their kinsfolk in the South, or from the vineyards of Men indistant lands. Hiding behind one of the largest barrels Bilbodiscovered the trapdoors and their use, and lurking there, listeningto the talk of the king's servants, he learned how the wine and othergoods came up the rivers, or over land, to the Long Lake.
The Hobbit: Chapter 9 - Barrels Out of Bond
Some of Thranduil's wine came from Dorwinion (translated by Tolkien as "The Young-land Country"), to the south of Dale, carried up along the River Running to Laketown. Presumably the best stocks are taken directly to the Elves with the remainder being sold to traders and locals at the town's extensive markets.
When he heard this Bilbo was all in a flutter, for he saw that luck was with him and he had a chance at once to try his desperate plan. He followed the two elves, until they entered a small cellar and sat down at a table on which two large flagons were set. Soon they began to drink and laugh merrily. Luck of an unusual kind was with Bilbo then. It must be potent wine to make a wood-elf drowsy; but this wine, it would seem, was the heady vintage of the great gardens of Dorwinion, not meant for his soldiers or his servants, but for the king's feasts only, and for smaller bowls, not for the butler's great flagons.
