You might query the New York State Military Museum at
http://www.dmna.state.ny.us/historic/mil-hist.htm

and the U S Army Heritage Education Center (formerly the U S Army Military History Institute) at
http://www.carlisle.army.mil/ahec/

for photographs of soldiers who served with the 159th NY Two other institutions which might prove helpful are the Brooklyn NY Historical Society and the NY Historical Society. In addition, query the Gettysburg Nat'l Military Park. Although the 159th did not see duty at Gettysburg, they have a tremendous photograph collection of individual soldiers.

There are some fine accounts of the 159th NY at Irish Bend in the Brooklyn DAILY EAGLE and the newspapers published in Dutchess and Columbia NY counties.

I've been researching Irish Bend for quite a few years and have turned up a number of accounts of the battle written by 159th participants.