Check out this site I made for a friend! USArtMap.com You can search for current, and future art exhibitions in the U.S., by artist, location, or a specific venue. It's much simpler than trying weed through typical search engine results, which can be stale, vague, misleading, broken links, or just deceptive advertisements.
I know, there are improvements that can be made to the site, and they will come as I have time to work on it. He had the data, and we wanted to put this together quickly to allow everyone to share in his extensive art exhibition db. He keeps updating the db on a weekly basis. Last I checked, there were exhibitions being tracked at over 5,000 venues across more than 850 cities.