The "Art" section of the "Weekend" guide of the Friday paper contains a listing of museum and gallery shows.
The auction houses in New York City have a number of fine arts sales throughout the year. Items for sale are displayed for three to five days before the sale and admission is free for the viewing. The auction houses run ads in the Friday and often the Sunday New York Times announces their upcomng sales. This information as well as images of the artwork for sale is available on their internet sites.