On the north coast, the two harbors where you might find somebody to give you sailing experience are Luperon and Samana. That is where the cruising sailboats are.
Problem with Luperon is that you would be sailing in the Atlantic and that can be very rough this time of year with the cold fronts coming down from the US. In Samana, you would have the option of sailing in the very large Bay of Samana, so that you could enjoy the sailing without fighting the conditions. The other option is to go out into the Mona Passage, and that is best on days when there is a weather window. During the winter, ther is no telling how long you would have to wait for one of those.
On the south coast, I'd contact Capt. Forest Rodriguez at Centro Marina del Mar
http://www.centromarino.net/